Coded Orthogonal Frequency Division Multiplexing
The Coded Orthogonal Frequency Division Multiplexing (short COFDM) is the modulation scheme used for DVB-T. Multiplexes many (e.g. QPSK- or QAM-) modulated signals in frequency domain.
COFDM is a quite sophisticated approach with many interesting qualities used in WLAN and DVB-T that transforms a block of a few thousand modulated signal samples via iFFT into the frequency domain and inserts well-known guard points into this spectrum.
Echoes and Multipath receiption effects will now disturb the signal, but due to the guard points the receiver can "equalize" these effects before the original signal gets recovered using a FFT.
it would be nice to have the links to the defining standards here as well as some pictures visualizing the concept, the "echo" and "multipath" terms and the interference problem. A more verbose explanation would be nice, too.