What is an aggregate bond ETF?

An aggregate bond ETF (often called "agg" or "core bond") is designed to represent a broad slice of the investment-grade bond market. Many track indexes that include Treasuries, agency bonds, mortgage-backed securities, and investment-grade corporates.

These ETFs are often used as a core bond allocation because they're diversified across issuers and sectors. But they still carry interest-rate risk, and their duration can be meaningful.

If you're using one as a bond core, check duration, the mix of government vs credit exposure, and how it behaved in rising-rate periods. Core bond ETFs can be steady in some regimes and bumpy in others.