Mobile ___ (3)
'mobile' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for movable that I've seen before include "Not fixed" , "Able to be conveyed from one place to another" , "Mobile" .)
(Other definitions for app that I've seen before include "Software item" , "Software for mobile devices, in short" , "bit of software" , "Program for a smart phone, in short" , "Software program for a mobile device" .)