“30-30” can mean different things depending on context:

• Sports (tennis): a score of 30–30, meaning both players have 30 points in a game.
• Baseball (30–30 club): a player who has hit 30 home runs and stolen 30 bases in a single season.
• Firearm: the .30-30 Winchester, a type of rifle cartridge commonly used for hunting.
• General math/notation: simply the number 30 and 30, often used as a ratio or comparison.

In short, it usually means a paired value of 30 and 30, with meaning depending on the field.