What do single quotation marks in the price of futures mean?

Cash bonds and futures based on U.S. Treasury securities do not trade in decimal format but in full percentage points, plus fractions of a 1/32 of par value.

(Source: Calculating U.S. Treasury Pricing)

The part after the apostrophe (single quote) is the fractional part of the price.

Let's take the bid price of 10-Year U.S. Treasury Notes Futures (ZN) as an example: 132'205. In decimal: 132 + (20.5 / 32) = 132.640625.

An example used to be provided on ZN's contract specifications page (archived webpage from June 2018):

For example, 126-16 represents 126 16/32 and 126-165 represents 126 16.5/32.

According to ZN's contract specifications, the minimum price fluctuation of ZN is 1/2 of 1/32 of one point. The smallest increment would result in a decimal price of 132 + ((20.5 + 0.5) / 32) = 132.65625, and the smallest decrement would result in a decimal price of 132 + ((20.5 - 0.5) / 32) = 132.625.