Definition
An order seeking execution at available prices without setting a specific price limit. It does not guarantee a fill price.
Hypothetical example
The last trade may be 100 while the ask is 101. A market buy may execute at 101 or another price.
Keep in mind
Fast moves or limited liquidity can increase the difference between expected and executed prices.
Official reference
www.investor.gov ↗Examples are illustrative assumptions, not investment recommendations.