Though the word gustnado sounds a bit like Texmex food it truly is a quite common feature associated to thunderstorm gust fronts. Gustnadoes, short for gust-front tornadoes, are small, weak and short lived spin-ups typically occurring on the leading edge of thunderstorm downdrafts, known as the gust front.
A storm's downdraft is caused by rain- or hail-cooled air flowing out of the thunderstorm and if it gets a little kink it will start to rotate, becoming a tornadic vortex. Now, if the gustnado picks up enough dust or debris it will be visible as a rotating debris cloud or dust whirl near the ground. They are in a way the little brothers of a tornado, only that you can get similar features without a thunderstorm present, e.g. along the leading edge of cold-fronts or air-mass boundaries.
Typically, they last for a few seconds and do not extend into the thunderstorm's cloud base. Whereas tornadoes (picture) are always connected to a thunderstorm's (or supercell's) cloudbase, commonly known as wall cloud. However, there are credible reports of gustnadoes developing a connection to the shelf cloud of a thunderstorm and lasting for 15 minutes or so. Therefore gustnadoes are frequently mis-reported as tornadoes, sometimes even in official storm reports.