Alignment: direction a person is facing. Good explanation here.
Closed position: partners are facing each other, shoulders are parallel.
Half open position: In rumba & merengue, partners are facing sideways, angle between partners between 90-180d, both hands are connected. Each hand is connected to the opposite hand (L of leader with R hand of follower, for example). Fifth position breaks in rumba & merengue utilize the half open position.
Double hand hold: Leader's LH holds follower's RH, leader's RH holds follower's LH.
Handshake hold: Leader's RH holds follower's LH.
LF: Left foot.
LH: Left hand.
LH hold: Leader's LH holds follower's RH.
LOD: Line of dance.
Open position: In waltz & merengue: partners are facing sideways, angle between partners between 90-180d, one hand is connected, one hand is free. The connected hands are opposites (L of leader with R hand of follower, for example). Crossovers in merengue & cha cha utilize the open position.
PP: Promenade position.
Quiet hand: Lack of movement in a hand, usually left one for the leader, implying lack of a lead.
RF: Right foot.
RH: Right hand.
S-a: Slow and.