Marking a location in the stream?

When comparing java.io.BufferedWriter to java.io.FileWriter, which capability exist as a method in only one of the two?

A) Closing the stream
B) Flushing the stream
C) Writing to the stream
D) Marking a location in the stream
E) Writing a line separator to the stream

A resposta correta é a E. Mas, o que a letra D quer dizer exatamente? Não entendi o que “marking a location in the stream” significa…