Safespot

A "safe-spot" refers to a place on the screen that you can place your ship to completely avoid damage from incoming bullet patterns. Safespots are typically the result of system exploits, game design oversights, or glitches/bugs.

Particularly egregious safespots can often allow a player to completely avoid damage while still damaging enemies and bosses for the duration of an encounter, which can completely nullify the difficulty of said encounter.