what does "declare" mean

[RoundTower]

It means you are playing high-low split. During the declare each player decides whether he is playing for high, low, or both halves of the pot. The declaration is either sequential (one at a time in clockwise order) or all at the same time. If you declare for low, you cannot win the high half of the pot, and vice versa; if you declare for both you forfeit the whole pot if you only have the best hand one way.

Hope this helps.