From Fidelity:
https://www.fidelity.com/learning-center/investment-products/fixed-income-bonds/bond-yield-curve
“A yield curve can refer to other types of bonds, though, such as the AAA Municipal yield curve, or reflect the narrower universe of a particular issuer, such as the GE or IBM yield curve.”
When discussing the Federal Reserve and the Funds Rate, the yield curve always refers to federal government securities.