The number 10 is an even natural number that follows 9 and precedes 11, and it forms the base of the decimal numeral system, which is the most common number system used worldwide. The decimal system likely developed because humans have ten fingers and toes, which were naturally used for counting. The word "ten" originates from the Proto-Germanic root *tehun, itself derived from the Proto- Indo-European root *dekm- meaning "ten".

Besides its numerical significance, "ten" is used in several contexts:

• A collection of ten items, such as ten years, forms a decade.
• The ordinal adjective related to ten is "decimal," and the distributive adjective is "denary."
• Increasing a quantity by one order of magnitude typically means multiplying it by ten.
• The term "decimate" derives from an ancient Roman practice of killing one in every ten soldiers as punishment.

In daily life, 10 is also associated with the highest school grade in some countries (e.g., the Netherlands), is relevant in sports (ten events in a decathlon), and the number 10 card is notable in card games. The number appears repeatedly in cultural, historical, and mathematical contexts and remains foundational to counting and arithmetic systems globally.