A relational symbol combining "less than" with "approximately equal to" to indicate one quantity is slightly less than another.
Examples
Comparing approximate numerical values
3.141 \lessapprox 3.142
Comparing sequences with a limit
a_n \lessapprox L \text{ as } n \to \infty
Comparing approximate inequalities in analysis
f(x) \lessapprox g(x) \text{ for } x \in [a,b]