1. The act of binding up or bandaging.
2. The manner in which something is bound up.
3. (Botany) An abnormal flattening or coalescence of plant parts, such as stems.
Etymology: from Latin root fascia, band.
The picture is from Wikipedia.
I first learned this word while investigating a variety of cherry tomato in my garden that had a tendency to produce double-wide fruit.
Apparently, plant breeders choosing for such a tendency created the beefsteak tomatoes we see today.
Standard tomatoes have an apical meristem (um...a tip where stuff like leaves and flowers can grow...any actual botanists, feel free to correct me), concentrated around a point, to produce a single, roughly cylindrical seed cavity.
Fasciation elongates or contorts the apical meristem, and over time this can result in the contorted, meaty interior of a beefsteak.
This NPR article explains it better ("if not for the control of one gene, the world might be overrun by giant tomatoes").