What is the difference between query optimization and boolean indexing in Pandas?

query() uses expression parsing and optional NumExpr optimization, while boolean indexing uses direct NumPy masks.

Boolean indexing evaluates conditions using NumPy vectorized operations and creates a boolean mask explicitly in Python space. query() parses string expressions into an internal evaluation tree and may use NumExpr to execute faster in compiled form. query() is often more readable and sometimes faster for large datasets.