Anyone who's been in the camera grind for a long time are familiar with the technical term "f-stop", sometimes also known as "f-ratio," "focal ratio," or "relative aperture". This stop is often used in still photography and still camera lenses. For the beginners, the f-stop setting in the camera is a determinant on how much light is allowed to enter the lens and pass through.
Meanwhile, there's the "t-stop". The letter "t" comes from transmission. The t-stop somehow similarly functions like the f-stop (as they are used in still photography), but unlike the f-stop, which is an equation (since it's actually a mathematical reading), the t-stop is an aperture measurement on cinema lenses. Now, we all know that cinema gear and lens are much likely more expensive than still camera lenses. Cinema lenses need critical accuracy, therefore more light in terms of power consumption, and more expensive camera sensors.
This is just an introduction for those who have no idea what these terms are. You can find out more about these two by watching the explanation below.
Preview image was taken from the video.