Britain and Canada standard spelling of fitness center.

(simile) To be a perfect fit, to be exactly the right size.

(mathematics) A line on a scatter plot that best defines or expresses the trend shown in the plotted points. It is chosen so that the sum of the squares of the distances from the points to the line is a minimum. It also illustrates the correlation (positive, negative, or zero correlation) between the plotted variables.

(idiomatic) At a very high volume; extremely loudly.

plural of line of best fit

(simile, Australia) In good physical health.

(Australia) a health indicator age in comparison to a person's true age, based on a survey of diet, exercise, and other factors.

(idiomatic) If a description fits, it is probably the case; if an insult accurately describes you, you must bear it; if you take offence at an insult that was only implicitly directed at you, you admit the insult is true enough to be recognizable.

(Britain) Alternative form of if the shoe fits, wear it

(medicine) Benign idiopathic neonatal seizures, a rare form of seizures that manifests in newborns in the latter part of the first 7 days of life.