You can easily arrive at this position via the QGD or the Slav as the Semi Slav Defense is a hybrid of the two. You can employ this system to take away the threat of the Exchange Variation. 5.cxd5 would not now give you anything to worry about.
This system will also give you a safe secure position in the face of 5.Qb3. White has to find something else to threaten your camp. Two systems of attack have emerged over the years as White's main hopes of establishing an advantage.
He can play 5.e3 which leads to the Meran Variation. Or he can run with 5.Bg5 which brings the game into the Anti-Meran Gambit. There your powers of accurate calculation would be tested to the full.
After 5.e3 Black can play several moves but your main choice should be 5...Nbd7. The main continuation is 6.Bd3 offering you the option of taking on c4. This you should do as after 6...dxc4 7.Bxc4 b5 you have reached the Meran Variation.
The position is very good for Black. Over the years people have tried just about every move but have failed to find a big edge for White. What exactly have you gained in exchange for your strong pawn on d5? The answer is space and activity on the Queenside. After 8.Bd3 a6 9.e4 you are in position to play the key pawn break ...c5.
This puts the question to White's proud center. If he takes on c5 his center is gone so he must advance one of the two pawns. White's main goals in this opening is to get a Kingside attack. So this counter play on the Queenside is Black's way of taking the sting out of the threat. Which pawn advance makes it harder for Black to weaken White's attacking potential? 10.e5 or 10.d5?
The lines after 5.Bg5 are known as the Anti-Meran Gambit as the c4-pawn is offered by White to Black in those lines. The lines after 5.e3 Ndb7 6.Qc2 are apparently known collectively as the Anti-Meran Variation.
These lines (after 5.e3 Ndb7 6.Qc2) are another way to avoid the Meran and should not be confused with the gambit lines after 5.Bg5. The difference from the Meran Variation being that after 6.Qc2 dxc4 7.Bxc4 White has an extra tempo with the Queen on c2 here. For this reason Black prefers 6...Bd6 over 6...dxc4.
The line then splits into two sub-variations on White's 7th move. The Karpov Variation begins with 7.Bd3. Now after 6...Bd6 7.Bd3 0-0 8.0-0 Black is okay. White has another option in the position though. He can play the Shirov–Shabalov Gambit starting with 7.g4 and as you can probably guess, things get a little messy.
The Karpov Variation starts with 7.Bd3 and White's plan is clear. He will castle Kingside and point his pieces towards Black's King, also typically on the Kingside. His light square Bishop and Queen stare down at h7 from behind his center. He will try to get his Knight close enough to strike.
Black won't sit back while all this is going on. After the inevitable ...dxc4 he has an expansive game on the Queenside. He plays ...b5 sometimes supported by ...a6. His light square Bishop will take up a great post on b7 after the ...b5 push.
His Queen and dark square Bishop form a battery against h2 and he has the ...c5 and ...e5 breaks in reserve that can be played at any time. An interesting battle will ensue with chances for both sides.
What if you find the Karpov Variation a little dry? Can you spice things up? Absolutely. The Shirov-Shabalov Gambit injects surprise into proceedings with 7.g4 out of nowhere.
Black can play this in many ways. He can take the Main Line and play 7...dxc4. You will then push on with g5, kicking the Knight out of f6 and causing mayhem on the Kingside. Tactical firefights will take place in the center and you will most likely castle long or even leave your King in the center.
In return for your initiative on the Kingside, Black will have play on the other wing and there is an ongoing battle for supremacy in the center.
Black can also play 7...h6 to prevent 8.g5. This may seem like a quieter way to handle things but the tactics get pretty wild in this variation. Black does not like accept the gambit with 7...Nxg4 because 8.Rg1 and the eventual Rxg7 is a little dangerous for Black although he can castle long in these lines.
If 5.e3 leads to the Meran Variation and this holds little promise for White, you need another way to play. 5.Bg5 leads to the Anti-Meran Gambit and some tricky lines to get command of. You need to learn some theory here. Wrong move orders leave you open to some real pain.
Here this line splits off into two main branches as Black has two very different ways to respond. The Moscow variation kicking off with 5...h6 needs a lot of homework. After 6.Bh4 dxc4 7.e4 g5 8.Bg3 Black has just enough time for 8...b5 to hold the c4-pawn. All of this without losing the Knight on a pin.
He can accept the gambit with 5...dxc4. This is the Botvinnik Variation. This option also requires a lot of preparation. The game is unbalanced both positionally and materially.
The main move now is 5...h6, kicking the Bishop. This is the Moscow Variation. The Bishop usually retreats to h4. The Bishop gets another prod by 6...g5 and after 7.Bg3, Black can take on c4 and shore up his prize with 8...b5.
So does White have enough compensation for his c-pawn? In recent years top players have become far more optimistic about White's position in this once scorned line. They have found that White's impressive center gives him good chances against Black's somewhat loose Kingside after 8.Be2.
This former sideline is now a well beaten path at the top table of world chess. It is heavily analyzed and rich in theory with many, many GM games. Several variations have sprung from this position and it pays to go to school before trying it in the field.
If you take on c4 you bring the game into the Botvinnik Variation. This is tactics central and even GMs have to study these lines before venturing into them in real time.
Things get really complicated. White will sacrifice a Knight on g5 for the g and h-pawns. This will allow the dark square Bishop to retain the pin on Black's f6-Knight. After 9...hxg5 10.Bxg5 Nbd7 we reach the main starting position in this variation.
It's not a real sacrifice of course as the e-pawn will take on f6 straight away. But White does sacrifice the other Knight for real in the Main Line. He does this for a strong attack on Black's still central King.