Back in the 60's and earlier a reverse was frequently considered to show 19 HCP and a game forcing hand, just like a jump shift. That style is only maintained by a small minority nowadays. The standard minimum for a reverse is now a decent 17 HCP, or 15/16 with a 5-loser hand, or 13/14 with a 4-loser hand. (if that concept is new you might want to find a book discussing the "losing trick count" -- there's a good one by Klingler.)
A reverse has no upper limit and is 100% forcing. It can be used by two-suited hands that contain game in hand, but could never be described after a 2-club opening.
Responses to a reverse are usually a source of confusion if there has not been at least a brief partnership discussion. There are numerous conventional methods to distinguish between good and bad hands by responder. The ones I've used are:
- Structured Reverses (with an artificial 2NT to show weakness);
- Lebensohl 2NT;
- Fourth Suit UNforcing. (it's really forcing, but is used in this convention to artificially show weakness; a rebid of opener's first suit is used if the fourth suit is beyond it)
The sad truth is that there is no "standard" response structure without discussion (other than a rebid of responder's major to show more than 4 cards). (BTW -- does anyone know what response structure, if any, is included in Bridge World Standard?)
A word on length is appropriate here. Reha posted a response saying that a reverse "tends" to show a longer first suit. He was being overly conservative. There are few absolutes in bridge. This is one: A reverse ALWAYS promises a longer first suit than the second. They are never the same length.
The above discussion applies to Standard American and its common, affiliated variants -- 2/1, Eastern Scientific, Walsh, K-S, Roth-Stone. It also applies to a "true reverse" -- a rebid by opener of a new suit at the 2-level that is higher ranking than the opening suit, and lower- ranking than partner's 1-level response. It does not apply to what is called a "high reverse" -- a response at the 3-level after partner's 2/1 response (e.g., 1H - 2D - 3C). In S/A this shows more than a minimum opening hand, but is not as strictly defined as above.
One thing you may want to clarify with a partner is whether the second suit must contain at least 4 cards, or can be made with fewer to provide the flexibility to gain more information from partner. This is integral to K-S, and is also used on the spur of the moment by many other players.