A Counter (Japanese: カウンター Kauntā; Chinese: 計數物 Jìshǔwù "Counting object") is a generic marker that can be put on cards. It is generally used on Monster Cards to note how many times a limited effect has been used, etc. Some cards use only a specific type of Counter (most commonly Spell Counters), but many use non-specific Counters.
There is no official way to represent a Counter. However, some of the most common ways include small objects like glass beads, paper clips, pennies/coins, and the numbers on a die.