Plasmodesma is a narrow thread of cytoplasm that passes through the cell walls of adjacent plant cells and allows communication between them.
Source: Coursera's Understanding Plants - Part II: Fundamentals of Plant Biology Week 1 1.7 The vacuole and plasmodesmata
URL: https://www.coursera.org/learn/plant-biology/lecture/gwRmz/1-7-the-vacuole-and-plasmodesmata