Connectivity or connectedness is a property that a group of cards can have describing how sequential the cards in the group are. For example, if the board cards in Texas Hold'em are close to one another in value, then they are said to be connected. High connectivity means the cards are sequential, like king, queen, jack. A low connectivity means the cards are not close to one another.
Straight draws are only possible with a high connectivity, and higher connectivity means more straights are possible. Hence, players like to play connectors like 78 in Texas Hold'em and Omaha since they make it easier to hit a straight.