Is Gibraltar in the EU single market?
Short answer
No. Gibraltar is outside the EU.
Detailed answer
Gibraltar left the EU with the UK and is outside the customs union and single market. There is however a new Treaty coming which will make significant details to the fluidity of movement of goods and people. Gibraltar will remain outside the EU but in a 'common travel area' with Schengen, and similarly for goods. There's a lot of detail yet to be understood, so watch this space.