What does "voiceless" mean?

Voiceless: (Phon.) Not sounded with voice; as, a voiceless consonant; surd. Voiceless stop (Phon.), a consonant made with no audible sound except in the transition to or from another sound; a surd mute, as p, t, k. -- Voice"less*ly, adv. -- Voice"less*ness, n.