Lesser Festivals are a type of observance in the Anglican Communion, including the Church of England, considered to be less significant than a Principal Feast, Principal Holy Day, or Festival, but more significant than a Commemoration.
Whereas Principal Feasts must be celebrated, it is not obligatory to observe Lesser Festivals.
They are always attached to a calendar date, and are not observed if they fall on a Sunday, in Holy Week, or in Easter Week.
In Common Worship each Lesser Festival is provided with a collect and an indication of liturgical colour.
Source: C of E website.