diff --git a/book/01-introduction/sections/what-is-git.asc b/book/01-introduction/sections/what-is-git.asc
index 466201b23..bc8ca2ca2 100644
--- a/book/01-introduction/sections/what-is-git.asc
+++ b/book/01-introduction/sections/what-is-git.asc
@@ -10,7 +10,7 @@ Even though Git's user interface is fairly similar to these other VCSs, Git stor
 
 The major difference between Git and any other VCS (Subversion and friends included) is the way Git thinks about its data.
 Conceptually, most other systems store information as a list of file-based changes.
-These other systems (CVS, Subversion, Perforce, and so on) think of the information they store as a set of files and the changes made to each file over time (this is commonly described as _delta-based_ version control).
+These other systems (CVS, Subversion, Perforce, and so on) think of the information they store as a set of files and the changes made to each file over time, which are referred to as "checkins" or "commits" (this is commonly described as _delta-based_ version control).
 
 .Storing data as changes to a base version of each file
 image::images/deltas.png[Storing data as changes to a base version of each file]