Random Access Memory (RAM) is the form of memory used for temporary data storage in all computer-based technology (including smartphones and tablets). Put simply: it is the memory that programs require to process their various tasks, and to store temporary information while in operation. RAM, in contrast to long-term memory, may be accessed in any order, which allows for information to be called up almost immediately. However, it is considered a 'volatile' form of memory, and thus cannot be used for long-term storage.
Generally speaking, the greater the amount of RAM in a device, the more processing can be accomplished at any one time, the more programs that can be running simultaneously, and the faster they will accomplish tasks.