The abbreviation FSL may refer to:
- Florida State League
- FMRIB Software Library
- Freescale Semiconductor stock symbol
- Free-space path loss or free-space loss (FSL) in telecommunications
- Finnish Sign Language
- French Sign Language
- French as a second language
- Friends' School, Lisburn, a grammar school in Lisburn, Northern Ireland
- Fleet Support Limited
- Fast Simplex Link, an interface by Xilinx used in the MicroBlaze soft processor
- Fluid Science Laboratory
- Forward Stocking Location, a term used in warehousing
- fsl, the from status line capability of a terminal in the Terminfo database