When used without any parameters, Measure-Object will return a value for Count, which is the number of items passed in using the pipeline, for example:

PS> 1, 5, 9, 79 | Measure-Object

Count     : 4
Average   :
Sum       :
Maximum   :
Minimum   :
Property  :

Each of the remaining properties is empty, unless requested using their respective parameters. For example, -Sum may be requested:

PS> 1, 5, 9, 79 | Measure-Object -Sum

Count      : 4
Average    :
Sum        : 94
Maximum    :
Minimum    :
Property   :

Adding the remaining parameters will fill in the rest of the fields (except Property):

PS> 1, 5, 9, 79 | Measure-Object -Average -Maximum -Minimum -Sum

Count       : 4
Average     : 23.5
Sum         : 94
Maximum     : 79
Minimum     : 1
Property    :

The value for Property is filled in when Measure-Object is asked to work against a particular property (instead of a set of numbers), for example:

PS> Get-Process | Measure-Object WorkingSet -Average

Count       : 135
Average     : 39449395.2
Sum         :
Maximum     :
Minimum     :
Property    : WorkingSet

When working with text, Measure-Object can count characters, words, or lines. For example, it can be used to count the number of lines, words, and characters in a text file:

PS> Get-Content C:WindowsWindowsUpdate.log | Measure-Object -Line -Word -Character

Lines    Words    Characters    Property
-----    -----    ----------    --------
    3       32           268