A buffer pool is an allocation of main memory allocated to cache table and index data pages as they are being read from disk or being modified. The purpose of buffer pools is to improve database system performance. Data can be accessed much faster from memory than from a disk; therefore, the fewer times the database manager needs to read from or write to a disk, the better the performance.
The configuration of the buffer pool is the single most important tuning area, since you can reduce the delay caused by slow physical I/O.