Lertap 5's main measure of test and scale reliability is coefficient alpha, also known as Cronbach's alpha. There are many other measures of reliability; the preceding topic discusses some of them. When a test with a cut-score is used, measures of decision consistency will often become primary indicators of test quality -- these measures are discussed in another topic.
The text by Meyer (2010) is a highly-recommended reference in all of these areas.
Coefficient omega is yet another measure of reliability, not discussed in Meyer's text. It has been shown that omega is a superior measure of reliability as it makes fewer assumptions; this is now widely acknowledged, but practical studies, such as this one, have found that alpha and omega will be generally not be noticeably different.
Users of Lertap 5 who'd like to compute omega might want to make use of a special Lertap macro, "Omega1". This macro will create a special 'csv' data file and a small text file with several lines of R code designed for use with the Psych toolbox from CRAN.