RE is a Regional Express, a regional train of German Rail, that doesn't stop in every station.
RB is a Regional Bahn, a "milk run regional train of German Rail, that stops at every station.
In Germany, RB and RE generally do not run outside of a single German state, or Land.
IC is a Intercity train, a fast express train that runs longer distances, spanning state borders, with fewer stops.
ICE is an Intercity Express, the fastest of the express trains, usually going between major cities in Germany with few stops.
RB, RE, and ICE are strictly German trains although ICEs often go into countries surrounding Germany. RB and RE are slower but less expensive, and often connect smaller towns to major cities with IC and ICE service.
Many countries call their express trains ICs.
TGV is a very fast express train originating in France, although TGVs often go into adjacent countries.
EST stands for EuroStar, which could be the train that goes through the chunnel from UK to France, Brussels, Amsterdam, and Köln. In Italy it would be the Italian EuroStar (ES*), the fastest train in Italy.