The whole periodic table is divided into four blocks. Groups 1 and 2 are called the s-block, because all the elements in those groups have electronic configurations ending is the s-orbital. For example, in Group 1, lithium has an electronic configuration of
The transition metals, from Group 3 to Group 12, are called the d-block. The elements in these groups have electronic configuration such that they end in the d-orbital. Example:
The elements from Groups 13 to 18 are called the p-block. They have electronic configuration that end in p-orbital. Example:
*n.b.: Helium is an exception. Although in group 18, its electronic configuration is
In between Group 2 and the transition metals, there is a narrow band of elements in the 6th and 7th periods. They are called the Lanthanides and the Actinides respectively. These elements are the f-block. Their electronic configuration always end in the f-orbital. Example:
Note, I haven't written the full electronic configuration. I've only shown the last part of the configuration for elements with large atomic numbers, because that's the only relevant part in your question.