Its a popular saying in the bond market “buy clean, pay dirty.” It means, you as an investor must learn about bonds pricing and how they accrue interest.
Bonds price may change due to varying interest rates or to the issuer’s credit rating.

The answer to your question is quite simple:
Clean price is nothing but the bond price without interest, and the dirty price is the bond plus interest.
This helps an investor to avoid confusion while you trade bonds.