"Drive" (ドライブ Doraibu) is referred to as the amount of drive checks your unit is able to peform while attacking. Aside from drawing effects and the draw phase, drive checks are the main way to increase the player's hand. By default, it's only one drive check per attack, however, it's possible to increase and decrease the number of drive checks (stated as drive+1 or drive-1/-2). In case of increase the drive check, you must check for the following drive after resolving all effects during the previous one. If your unit's drive check becomes 0 or less, then no drive check can be performed.
Vanguards with the ability to stand themselves occasionally get a drive-1/-2 as a way to prevent the player from drive checking too many cards. This has become more commonly seen in "Stride" G units.
By default, only your vanguard (or Legion Leader in such case) is able to perform drive checks during the drive step of your battle phase, but it's also possible make that your rear-guard performs drive checks. In that case, the drive step applies to that unit.
A drive check is done due to the following form: Put the top card of your deck into trigger zone face up, if that card has a trigger effect, resolve all its actions immediately, in any order. After that, resolve all abilities that were activated by the drive check in any order, and if the card is still in the trigger zone, put that card into your hand. After completing all actions, repeat this process as many times as the number of your attacking unit's drive checks.
In Skill Icons
Currently, there are two skills which modify the normal amount of drive checks.