Hallux:

In most birds, the digits (toes) I through VI are present (we have five digits, numbered I through V).  In most birds, the first toe is usually directed backwards, and the other three point forward, and this is technically known as the anisodactyl foot.  However, in parrots, digits II and III point forward, and digits I and IV are directed backwards.  This type of foot is called the zygodactyl foot.  Swifts have a foot adapted for climbing, and all four toes point forward, and this is called the pamprodactyl foot.  Emus, rheas, many wading birds and some woodpeckers only have three functional toes, and in most of these birds, it is the first digit (the hallux, which is similar to the big toe of man) that is lost.  The ostrich has only two toes, with digits I and II being lost.

Reference:  http://www.exoticpetvet.net/