A measure rest looks like a whole rest, but is centered within a measure and indicates that the entire measure (or a voice within it) is silent:
It is commonly used in all meters (except 4/2 and 8/4).
A multimeasure rest is used to indicate a run of empty measures, the number of measures being shown by a figure above/below the staff.
Multimeasure rests can be turned on/off with the shortcut M, or by checking "Multimeasure Rests" in Format→Style…→Rests.
By default, if multimeasure rests are enabled, any sequence of two or more empty measures is automatically converted to multimeasure rests.
To change the minimum number of empty measures needed to trigger multimeasure rests:
Multimeasure rests can be turned on/off independently in the score and instrument parts.
Multimeasure rests are automatically broken at important points, such as double barlines, rehearsal marks, key signature or time signature changes, section breaks etc.
However, you can opt to break a multimeasure rest elsewhere as follows.
You can edit properties specific to multimeasure rests in the Multimeasure rest section of the Properties panel:
Show number: This box is checked by default. Uncheck it to hide the multimeasure number.
Number position: Adjust the vertical position of the multimeasure number, above or below the rest.
Some global properties of multimeasure rests can be set from Format→Style…→Measure numbers:
Others from Format→Style…→Rests:
Other measure-related pages: