Ask
Basics
What it means
The lowest price a seller is currently willing to accept. It is the price you pay if you buy right now.
Example
If AAPL shows an ask of $150.05, a buyer using a market order to buy 1 share pays $150.05 per share.
Mistake beginners make
Beginners assume the price on the screen is what they pay, then are surprised the fill comes in at the ask, which is always slightly higher than the mid price they were watching.