JF Before yose you pay attention to ijime. This means teasing/bullying but in go it refers to the free sente moves you get by playing against weak positions.
When amateurs talk about thickness they also talk about moyos and influence. When pros talk about thickness they talk instead about ijime, especially the highly desirable state of not having to worry about being ijime-ed.
There is a good example, as I recall, in Fundamentals of Go of the appalling damage that can be done. I would suspect that in a large number of the case where a move is ignored locally, it is in fact answered at the other end of the territory. Anyway, main point is that ijimeru is a useful concept if you want to tune into high-level discussions of go. Nerai is another, which Charles was going to write up...?
Charles I've moved this away from the endgame page it started life on, so that some of these concepts can be separated out.
First, I know about yoritsuki as the way to take profit from the opponent's weak groups. Assuming the early endgame has started we can assume that with correct play weak groups don't die. But it is profitable to attack them, if one can find the direction of play. That I understand as yoritsuki, as a counter to the amashi strategy.
So, in what way does ijime relate? From what John writes above, it could be a more general concept, including 'weak territories' with open skirts.
There is also an example in Kage's Secret Chronicles more directly related to the question of allowing your opponent to play 'at both ends. I must confess I didn't take the point when I last looked at it, a while ago.
As for nerai, I think I put it in a mental pigeonhole after hearing John speak about it. Roughly speaking, a 'target': for this page, something worth taking gote to prevent your opponent having the chance to do? I remember coming up with the equation virtual groups = invasion nerai.
Aha - maybe ijime is to yoritsuki more like nerai is to aji.
JF While not wanting to stunt creative thinking, I would strongly recommend not making any connection between ijimeru and yoritsuku. There is a class of words that are used over and over again in go, but are really just words in the ordinary language. Most people are reluctant to count these as technical terms. "Attack" is an obvious example. For most Japanese yoritsuku and ijimeru probably fall into this category. Yoritsuku, indeed, is not very common, rare even - many writers find it too vague. It lacks nuances. It just means "approach", "getting access to" I would recommend westerners to forget it.
Ijimeru may likewise be only a quasi-technical term, but in contrast it is very common, and it has juicy connotations: persecution, tormenting, forcing someone to watch Big Brother or the Eurovision Song contest, etc. If someone wants to look them up, here are some concrete examples: (1) Kitani-Fujisawa (GoGoD reference 1961-09-20a), B109 etc 1961-09-20a; (2) Otake-Fujisawa (1981-02-04a), , 42 and 106 (this 106 effectively wins the game, by the way).
Here is a quotation from a book on thickness. "The procedure to convert thickness into territory is to attack, When such attacks are locally severe, it is called ijime (tormenting). If there are many positions where you can do this tormenting, at some point the balance of territories will shift in your favour." (The context is explaining that thickness gives up profit initially in the expectation of clawing it back later.)
To explain to others the allusion to nerai: although unfamiliar to most westerners, it is by far the commonest technical term in high-level discussions of fuseki. It came up on a BGA Strong Players Training Day in a session to do with trying to understand top pro thinking by using the words they use. The mismatch between pro and ama vocabulary is rather stark. You say aji, they say nerai, you say influence they say thickness, There's a high incidence of words like mamoru and ijimeru (and, related to this, tsurai), yuuryoku is very common, moyou is rather rare, etc, etc. Realigning the registers could be a major step forward.
Kageyama teaches that treating unthinkingly as sente leads to being pushed around (which is the same fundamental point as Bill makes on said page).
Bill: Thanks, Charles. :-)