short for Do It Yourself.
also see this interesting article about different local cultures of repair of mobile phones:
..."Repairs are often carried out with little more than a screwdriver, a toothbrush (for cleaning contact points) the right knowledge and a flat surface to work on. Repair manuals (which appear to be reverse engineered) are available, written in Hindi, English and Chinese and can even be subscribed to, but there is little evidence of them being actively used. Instead many of the repairers rely on informal social networks to share knowledge on common faults, and repair techniques..."