The yearly fee a mutual fund charges, as a percentage of what you hold, taken out of the NAV.
The total expense ratio covers the fund's management fee, its running costs and, in a regular plan, the distributor's commission. It is deducted a little each day, so it never appears as a charge; it shows up only as a lower NAV.
A direct plan and a regular plan of the same scheme hold the same portfolio. The direct plan's TER is lower because it pays no commission, and over many years that difference compounds into a noticeable share of the final corpus.
Figures on this page are filled from the same tax and scheme tables the calculators use, for the current financial year. Every term in the glossary.