All the possible combinations of a number of selections. In other words this amounts to the total number of ways in which you can combine your selections. For four selections, 1,2,3,4 you can combine the horses as follows: one four-times win bet (1234), four win trebles (123, 124, 134, 234), six win doubles (12, 13, 14, 23, 24, 34) and four win singles 1, 2, 3 and 4. These permutations are used in bets such as Lucky 15, Lucky 31 and Lucky 63, Trixie, Yankee, Canadian, Heinz, Super Heinz and Goliath.
It is possible to 'perm' selections. E.g, if you have made 3 selections (A, B and C) you can 'perm' every possible double. In this case, all the doubles possible are AB, AC, and BC making a total of three bets. If you have made 4 selections (A, B, C and D) you can also 'perm' all the possible doubles from these four. Now the doubles are AB, AC, AD, BC, BD, CD; a total of six bets.
A combination of available outcomes.If you have made 3 selections (x, y and z) you can perm all the possible doubles. In this case all the doubles possible are xy, xz and yz; a total of 3 individual bets or lines.You can have any number of perms, ie.any 8 from 10 = 45 bets.