Definition of gaper
When we talk about "gaper", we are talking about a hole in one hand, the hole in the sequence. The expression is used to talk about the private cards we receive preflop. If we receive 7-8, we talk about connectors. If we receive 6-8 or 7-9, we will speak of "gaper" in this case, from 1 gaper (a hole from 1 to the sequence). We can also describe a hand as 6-9 of "two gaper". gaper's are generally less interesting to play than connectors because they will hit less flop, but they should not be underestimated.
Some gapers dominate connectors
A hand like 9-10 heart is a matching connector. We know that this type of hands will play very well. Against a random hand, this hand will have 54% equity. If we now take a one-gaper (J-9 heart), we have a matching gaper rather than a connector, but we now have 55.6% equity against a random hand. We'll generally refer to this hand as a "one gaper" or "two gaper". The expression "three gaper" could be used, but it is almost never used (three gapers are not as strong as one gapers or connectors). The gapers are also hands that will make straights less obvious to your opponents.