Due to the comments I found the answer (the problem was that on the web it is referred to always in French, and not English, hence it is virtually undiscoverable, except for French speakers) wikipedia:
“The Séminaire Nicolas Bourbaki (Bourbaki Seminar) is a series of seminars (in fact public lectures with printed notes distributed) that has been held in Paris since 1948. It is one of the major institutions of contemporary mathematics, and a barometer of mathematical achievement, fashion, and reputation. It is named after Nicolas Bourbaki, a group of French and other mathematicians of variable membership.”
A Bourbaki talk is always given by a speaker about other people’s work. It is accompanied by an expository paper explaining difficult recent material.