How do you define a small card in a texas holdem preflop hand? In the book "Holdem poker for advanced players" by Sklansky and Malmuth on page 14, they mention that "an x represents a small card". They do this in the context of giving preflop hand rankings i.e. a particular preflop hand is Ax which is ranked similar to KJ.
A small card, sometimes called a "rag", is usually any card that isn't a face or paint card, which includes the 10. So anything from the 2 to the 9 may be considered a small card, although some players may consider the 7 through 9 as medium cards.