A lectionary is a collection of scripture readings assigned to specific dates. In the Christian tradition, we have a concept of a year that starts with Advent and ends with Easter. There are several different approaches to lectionaries, but the most common is called the "Revised Common Lectionary." This lectionary is used by several different Christian traditions, but it is not the only lectionary. Some are annual and others, like the RCL are broken into a cycle that reset every number of years.