An alias is a way to subsitute a list of itemid's for ease and convienence.
Consider this rule:
noIronTools: actions: [USE] xp: min: 3 items: restrict: - 256 - 257 - 258 - 267 - 292 - '17.2'
That list can give you number blindness. That is where aliases come in. In your config, you can list item ids and then refer to them by their alias:
aliases: woodenEquipment: [268, 269, 270, 271, 290] ironEquipment: [256, 257, 258, 267, 292]
Then the above rule will can look like:
noIronTools: actions: [USE] xp: min: 3 items: restrict: ['ironEquipment']