SQ, Sq, or sq may stand for:
- Sentience quotient, a measure of the total processing capacity of a brain
- Shqip, the Albanian language (ISO 639 alpha-2 code)
- Singapore Airlines (IATA airline designator)
- Social (intelligence) quotient, a statistical abstraction of social intellegince
- Sound quality, the characteristics of the output of a preamp, amp or sound system
- Space Quest, a series of adventure games by Sierra Entertainment
- Spiritual quotient, a term in popular psychology
- SQ (program), a program for compressing files on MS-DOS and CP/M
- Square, a type of measure of area, such as square foot (sq ft)
- Status quo, Latin for "current situation"
- Stereo quadraphonic, a matrix quadraphonic gramophone record format developed by CBS
- Subcutaneous injection (abbreviation based on pronunciation)
- Sûreté du Québec, the Quebec police force
- Systemizing quotient, a measure of a person's neurological tendency to systemize
SQ(squeeze) was a program used in the early 1980s on both DOS and CP/M computer systems to compress files so they use less space, devised by Richard (Dick) Greenlaw(?) circa 1981. Files compressed by SQ are identified by changing the middle initial of the extension to "Q", so that text files ended with the extension .TQT, executable files ended with the extension .CQM or .EQE, documents with .DQC, etc. SQ used static huffman coding as the compression algorithm.
Groups of files were often combined into an archive using the LU program, which created .LBR files containing all the files needed for a particular group, such as all the files needed to install an application. Typically such files were either individually compressed (because LU did not compress files) or the LBR archive was itself compressed with SQ (similarly to the use of tar and gzip together in more modern times).
With the development of the ARC program (which combined both compression and archiving into one program) and its ARC archive file format, SQ essentially became obsolete on most systems, except CP/M, which lacked an ARC port for several years. On CP/M systems, the CRUNCH compression program was written to implement the LZW algorithm (as ARC did) and plug the gap.