What type of cable is this? I found it in the wall without any junction box just taped off at the end with electrical tape.
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It's a data cable.
Probably CAT5 or CAT5E grade. (it will be written on the blue jacket every metre.)
These cables are used for ethernet (between computers and routers) and for connecting telephones, and home automation equipment, intercoms, thermostats etc. I'm guessing there used to be a phone jack there.