Mining is a terminology used in cryptocurrency for verification of transactions. Those who do mining are called miners. For mining one needs a mining device and a software which is available online and needs high speed internet. There are millions of miners earlier but these days their number is getting decreased in case of bitcoin mining. Because mining is also getting advanced from simple mining to pool mining and then pool mining to cloud mining, All the mining needs advanced system, 24 hours electricity, high speed internet of 100 mbps + and moreover continuous maintenance of all devices.
Every coin is designed on several aspects and are total number of coins, block rewards. With the increase in mining and supply of coin, their difficulty gets increased and hence the process of simple mining has changed to pool mining. In pool mining, several miners join the network in order to verify the transaction and the reward is equally shared but with the increase in further difficulty, this concept is now become more advanced and is called cloud mining.