Tempo:
In
chess,
tempo refers to a "turn" or single move. When a player achieves a desired result in one fewer move, the player "gains a tempo"; and conversely when a player takes one more move than necessary, the player "loses a tempo". Similarly, when a player forces their opponent to make moves not according to their initial plan, one "gains tempo" because the opponent wastes moves. A move that gains a tempo is often called a move "with tempo".
I can describe tempo with R.O.B.. While he's in a grab combo after using his laser, he is gaining tempo. This is because he is damaging his opponent
and charging his laser at the same time. His opponent isn't moving any slower, it's just
R.O.B. is moving faster. Tempo is similar to covering options or forcing an opponent to make a certain move.
Another example is Ike. If his opponent is on the ledge Ike space himself just outside of get-up attack range and begin to charge an up-smash, Ike isn't gaining any tempo, (well, he technically is) but
he's forcing his opponent to lose tempo. If his opponent uses any option that will get-up on the stage, (get-up, get-up attack, jump, or roll) they will get hit by the Up Smash and Ike will win the trade. The only option his opponent has is to drop off the ledge, but in this case
Ike still has more tempo. Why? Because his opponent no longer has ledge invincibility and is vulnerable to attack.