"Unit" in Measurement
In Measurement we talk about "Units" ... what are they?
A unit is any measurement that there is 1 of.
So 1 meter is a unit.
And 1 second is also a unit
And 1 m/s (one meter per second) is also a unit, because there is one of it.
And so on ...
Standardized
Units of Measurement are "standardized", meaning that there is a welldefined standard way to measure 1 of them.

Example: For many years (1889 to 1960) there was the International Prototype Metre bar to show people exactly what 1 meter was.
But that wasn't accurate enough! Now "1 Meter" is defined as how far light travels in ^{1}/_{299,792,458} of a second. 
Without a Number
It is also common to drop the "1" in front and just talk about the type of measurement as a unit.
Example, in the metric system these are the most common units:
So "Unit" is a general term that means the type of measurement (and people understand that you mean just "1" of it)
So a conversation might go like this
Alex: "It measures 100"
Sam: "In what Unit?"
Alex: "Centimeters"

Example:
What unit does this Speedometer measure?
It measures km/h (kilometers per hour)
So the speed shown here is 220 kilometers per hour 
