A limit raise is made when responder wants partner to bid game if partner is near the top of his range and otherwise to pass (or correct to the lowest level of his trump suit when the raise was artificial).
Limit raises can be made by the partner of either opener or overcaller.
A natural limit raise is simply a jump response in partner's suit, such as 1-(P)-3 or 1-P-3 (but see Inverted Minors where that sequence is weak rather than a Limit Raise).
Over a take-out double, 2N is used as a limit raise in SAYC so that a jump to 3 can be used preemptively with a weak hand. This artificial raise is known as Jordan 2NT.
Over a suit overcall, in SAYC, 2N shows a balanced hand and is game invitational in Notrump, thus a jump in the suit is a limit (game-invitational) raise in the suit. A cue bid is used as a game-force raise with interest in slam, as well as first or second round control in the opponent's suit.
Again, the previous paragraph applies to SAYC. Others may play a cue bid as a limit raise or 2N as a limit raise over any 1-level overcall.
Number of Trumps Required
In SAYC, as well as other systems, a normal raise of 1 requires a minimum 5-card support, since 1 might be opened with only 3.
A normal raise of 1 requires a minimum 4-card support since 1 (particularly in SAYC) normally is opened with at least 4. (When 3-3 in the minors, 1 is opened.)
A strong (game invitational) raise normally shows extra trump length. For example, a simple raise of a major shows at least 3, while a limit raise shows at least 4.
If this were applied to the minors, then a limit raise of clubs would show at least 6 and of diamonds, 5, but for whatever reason, this is not done. In fact, Bobby Wolff, in one of his newspaper columns, says to make a limit raise in Clubs with only 4(!) -- AQ4 Q53 A86 K962.