I am reading a transcript of a talk given by a Tibetan lama, and the word 'sur' is used. What is it? Does it have something to do with food offering?
sur = burnt food offering (Wylie transliteration = bsur). See https://en.wikipedia.org/wiki/Sur_offering
It's difficult to answer this question without the context of the word use. The Tibetan and Himalayan Dictionary defines sur (སུར) as meaning "to whom", but in combination with other words it has totally different meanings, for example sur dug (སུར་དུག) = disease, and kha sur (ཁ་སུར) = date tree.
"Tsok" is a Tibetan Buddhist feast offering, could that be what is meant? See the Rigpa Wicki explanation.