Is mining something specific of Bitcoin?
Earlier cryptocurrency systems (which predated Botcoin) relied on a central clearinghouse to prevent fraudulent transactions, such as double-spending.  One of the objectives of Bitcoin was decentralization.  To prevent double-spending without a central clearninghouse, blocks of transactions need to be mined.  The process of mining requires a significant amount of computational effort to be expended by the miner.  Other nodes on the network will not recognize a mined block of transactions without this proof of work.