"Free testosterone" refers to the amount of the hormone testosterone that is readily available for the body to use. It is not bound to proteins and can easily interact with cells to carry out its functions. Full definition
I am always suspicious of free testosterone levels when they aren't specifically reported as a calculated free T. (tctmed.com)
Natural testosterone boosters also help to increase the amount of free testosterone in the body. (theathleticbuild.com)
You will definitely want to look at your calculated free testosterone levels before making any judgments about whether you are truly «high» or not. (tctmed.com)