from Kyabje Gelek Rimpoche's extended commentary on the Lama Chöpa:
Lama and Guru are synonymous; one is Sanskrit, the other Tibetan. What does Guru really mean? You may call it master, friend, Dharma-friend, Dharma-guide, or mentor. You can say these sorts of things in English, but the word Guru or Lama is supposed to mean ‘heavy in quality’.
Chöpa or puja means offering, offering as a practice, as a spiritual exercise. If we say ‘offering’, we may think of giving, but here there are a number of different offerings: outer offering, inner offering, secret offering, suchness offering, practice offering. Particularly important is the practice offering, which is not necessarily giving something. Also look at the six paramitas: the paramita of generosity is not necessarily giving. There are three types of generosity (generosity of giving material things, generosity of protecting against fear and generosity of sharing the Dharma), and generosity is also applicable to all other paramitas: there is generosity of morality, generosity of patience, generosity of enthusiasm, generosity of concentration, generosity of wisdom. So, regarding chöpa, you should think of a lot of different ways of offering, which will come a little later.
Choga means ritual. You say words, get the message behind the words, and think about the message. Actually, choga means yoga, too. The word choga is only applied to practices that deal with Vajrayana, not to pure Sutrayana, with the exception of the Medicine Buddha practice. Mostly, the word choga or yoga indicates that it deals with Vajrayana.
See Also: Author of Lama Chöpa