RER

Etymology
From, often reinterpreted as "Regional Express Rail".

Noun

 * 1) A type of railway system that generally runs from suburbs or satellite towns into a city centre, with a central tunnel or overground corridor with higher speeds and more widely spread stations than a subway or metro.

Proper noun

 * 1) Any of many RER systems in French-speaking countries.
 * , a project to improve commuter rail in Ontario.

Etymology
Réseau Express Régional (Regional Express Network)

Proper noun

 * , a Parisian tram, train and bus system

Noun

 * 1) A commuter rail or overground system, especially one with relatively high speeds and widely-spaced stations in urban areas.