INITRANS and MAXTRANS explained

Could you explain to me in detail about INITRANS and MAXTRANS? Books I've read on this topic are not clear.
 

Oracle stores information about row locks in the database block containing the row. The structure containing the information is known as the Interested Transaction List, or ITL. The ITL contains the ID of the transaction that has modified (and therefore locked) a row, and the ID of the row. Space for the ITL in each block is reserved at block creation time, based on the INITRANS and MAXTRANS parameters. INITRANS specifies how many "slots" are initially allocated in a block's ITL. When the number of transactions affecting a single block exceeds the number of existing ITL slots, Oracle will allocate space for more slots if possible, up to the value of MAXTRANS.