Target Pixel Files (TPFs) are a file common to Kepler/K2 and the TESS mission. They contain movies of the pixel data centered on a single target star.

TPFs can be thought of as stacks of images, with one image for every timestamp the telescope took data. Each timestamp is referred to as a cadence. These images are cut out ‘postage stamps’ of the full observation to make them easier to work with.

TPFs are given in FITS files, which you can read more about here. Lightkurve includes tools for you to work directly with these files easily and intuitively.