Five cards (not four) with values that are consecutive is called a "Straight". For example: 6, 7, 8, 9, 10. Keep in mind that the usual order of card values is: A, 2, 3, 4, 5, 6, 7, 8, 9, 10, J, Q, K -- (but see the "important note regarding aces", below.)
This is an example of a "straight":
These cards are consecutive (8, 9, 10, J, Q), so it is a "straight".
With straights, the Ace behaves strangely. It can be used either as the "low end" or as the "high end", but not both. See the examples below:
This is a straight:
This is also a straight:
However, the hand below is NOT a straight!!
Again, the hand above is NOT a straight.