I occasionally see annotations/commentary where a move / line is said
to make (for example) white win "by force". I am unsure if it has the
general sense of "this move initiates a forcing sequence where white
will come out on top" or something more specific, say, "with this
move, white exerts indefensible pressure ('force') on a particular
square / sector (say more attackers than defenders on f7 with further
defense impossible) that will give them victory."
What exactly does it mean?
The bold part is correct answer.
Forced move is exactly that: A move you are forced to play. A forcing move is exactly that: a move that forces the opponent to respond in a specific way, limiting his freedom of choice.
Take Alekhine's defense as example. White is forcing the exchange of knights, while Black is forced to exchange the knight:
[Title "Demonstrating difference between forced and forcing move"]
1.e4 Nf6 2.e5 Nd5 3.c4 Nb6 4.c5 Nd5 5.Nc3 Nxc3 6.dxc3
The italic part in my quote of your question is never called "force". The term pressure is commonly used to describe it, like in this example:
[Title "White to move"]
[fen "r4r1k/pp2qppp/6b1/8/2B5/1QP5/PP3RPP/5R1K w - - 0 1"]
So in this example we can say something like this:
White exerts decisive pressure on
f7 square, which might lead to a forced win for him if he now plays
1.Bxf7 Black is forced to exchange all the pieces ( other moves are even weaker for him ) after which the endgame is won for White. That is why we say White has a forced win: he can force Black to enter a lost endgame.
Hopefully this clarifies things. If you have further questions leave a comment.