What's the definition of a blockstring?

[Alfonse]

The term keeps popping up in each character's strategy guide, what are they and what are they used for?

On top of that, are IADs the diagonal cross-screen jumps?

[ennvi]

Block strings are simply combos used when your opponent blocks your hit confirming hit (usually A). I dunno if stopping the attack to continue pressure (like with miyakos 5a, 5b, 6b, 2a xx 5b, 6b...) counts as a single block string or multiple ones.

As for the diagnal jump, that's super jumping. IAD stand for instant air dash. It doing an air dash right after you jump.

[ikusat]

A blockstring is basically is a series of attacks used to put pressure on your opponent and create openings.

A very simple example of this can be found with V.Sion: 2A 5B -> ...
In this example, there are two common followups:
6B: this is an overhead attack and must be blocked high
2B: this is a low attack and must be blocked low

However, not all characters have the luxury of having an easy overhead attack, so most must use staggered attacks to create good blockstrings.  The purpose of a staggered attack is to create a frame trap - a small period of time where the opponent is actually free to act, but any action aside from blocking will get punished.

Let's take another simple example with Nanaya: 2B 5A -> ...
2B hits low, and if blocked low will guarantee that the 5A will whiff.  Here are some common follow ups to this example:
2B 5A: Repeating the same string will likely stuff any attack attempts or chicken block attempts
5C... : If 5C is cancelled from 5A, it will also likely stuff attacks, as well as chicken block
See a pattern here?  From these examples, it might seem that you have to block.  However... another common follow up is:
Dash throw: This beats blocking.

You might notice my examples above are all short.  This is because a fundamental part of a good blockstring is not being predictable.  You have to mix it up to always keep the opponent guessing: Do I block high or low?  Do I block or attack?  Can I jump out of this?

And that's what a blockstring is in a nutshell.

As ennvi said, IADs are instant air dashes, dashing right after you jump(966 for example).  Those "diagonal jumps" you are talking about might be super jumps, performed by a crouching motions and then a forward jump.  So 29 would give you a super jump.

[Alfonse]

Yeah, those fast diagonal jumps that leaves trails behind your character, Arcueids use that pretty often 

[Psylocke]

For Arc's case, it's a special superjump that she gets when tapping ground 5cc on an airborne opponent.  The 5c is the actual hit, the 2nd 5c makes her go into the special superjump.

ikusat pretty much covered it, but I'd also like to add that another option in blockstrings is re-dash in pressure.  Basically, what this means is that blockstrings have a natural end to them due to the opponent getting pushed out farther when blocking, so after a while the guy blocking will eventually be out of range of most of your normals, so in that situation it's pretty safe for him to backdash/jump away.  So re-dash in pressure is a big part of blockstrings too, since they will put you back into range where most of your normals will hit.  Normally re-dashins would be done off a move with frame advantage or off a move where it would be generally better for your opponent to continue blocking, since dashing back in constitutes a risk for the guy on offense, as he/she is vulnerable during forward dash startup.  This doesn't really apply to characters in the game with non traditional dashes(Satsuki, Nero, White Ren) but they have alternate ways of pressuring to the same effect.

[Alfonse]

Thanks for all the replies