'eight-foot' is a compound modifier or a compound adjecitve. Compound modifiers are combinations of words that work together to modify or describe a noun. In the case of 'eight-foot,' it describes the length or height of an object or entity.
when used before a noun, it should be hyphenated to avoid confusion. It's not typically used after the noun it modifies, but if it is, the hyphen is usually dropped and the term becomes 'eight feet.'
They installed an eight-foot fence around the property.
The room had an eight-foot ceiling, making it feel spacious.
The snake was an impressive eight-foot long.
always use a hyphen in compound modifiers like 'eight-foot' when they come before the noun they modify. This helps clarify that the words work together as a single descriptor. Avoid mixing singular and plural forms. For instance, 'eight-feet fence' would be incorrect. Instead, use 'eight-foot fence.' When expressing the measurement in a non-modifying context, you'd typically use the plural form without the hyphen 'The fence is eight feet tall.'