Iktara, or sometimes ektara, is a string instrument, but the most interesting thing about the instrument, as the name suggests, is that it has just one string. It gets more clear when you break the word into two parts, ik and tara. Ik or ek means one, while taar is a wire or string. Hence, Iktara is a single-stringed instrument.
Iktara was the instrument of well known devotee of Lord Krishna, Meerabai. Presently, iktara is mostly used by Punjabi folk artists. That also explains why it's popularly iktara and not ektara, as in Punjabi, one is ik, while in Hindi it's ek, with a slight difference.