The terms element family and element group are used to describe sets of elements sharing common properties. Here's a look at the difference between a family and a group.
For the most part, element families and element groups are the same things. Both describe elements that share common properties, usually based on the number of valence electrons. Usually, either family or group refers to one or more columns of the periodic table. However, some texts, chemists, and teachers distinguish between the two sets of elements.
Element families are elements that have the same number of valence electrons. Most element families are a single column of the periodic table, although the transition elements consist of several columns, plus the elements located below the main body of the table. An example of an element family is the nitrogen group or pnictogens. Note that this element family includes nonmetals, semimetals, and metals.
Although an element group often is defined as a column of the periodic table, it's common to refer to groups of elements that span multiple columns, excluding some elements. An example of an element group is the semimetals or metalloids, which follow a zig-zag path down the periodic table. Element groups, defined this way, do not always have the same number of valence electrons. For example, the halogens and noble gasses are distinct element groups, yet they also belong to the larger group of nonmetals. The halogens have 7 valence electrons, while the noble gasses have 8 valence electrons (or 0, depending on how you look at it).
The Bottom Line
Unless you're asked to distinguish between the two sets of elements on an exam, it's fine to use the terms 'family' and 'group' interchangeably.