Lehman Aggregate Bond Index

What Does Lehman Aggregate Bond Index Mean?
An index used by bond funds as a benchmark to measure their relative performance. The index includes government securities, mortgage-backed securities, asset-backed securities and corporate securities to simulate the universe of bonds in the market. The maturities of the bonds in the index are more than one year.

Investopedia explains Lehman Aggregate Bond Index
The index constructed by Lehman Brothers is considered to be the best total market  bond index, as it is used by more than 90% of investors in the United States. Along with the aggregate index, Lehman also has bond indexes tailored to European and Asian investors. This index cannot be purchased, but it is tracked by bond index funds; there also has an iShare exchanged-traded fund (ETF) that tracks the index. The Lehman Aggregate Bond Index trades on the PSE under the ticker AGG.