Early game attack with all available units to overwhelm early defenses of enemy.
Usually considered a low-quality surprise tactic to counter fast tech-up.
Games which don't allow countering rushes with defensive structures usually concentrate on preventing the rush units from reaching the base(trap/blocking walls/mining).

1.Very early: Attacks with a small group of earliest ground units without upgrades.
Easily countered with few defensing structures and terrain blocking.

2.Early: Attack with moderate-size group of early/earliest available units:
Countered same as above with optionally more defense structures or extra combat units.

3.Late Swarming: Attacks with large groups of early to mid-tier units with low upgrades:
Countered with own units, traps/mines and superior upgrades/tech level.

4.Midgame attacks are not considered rushes, as both sides have developed to mid-tier tech/units and created defensive lines.