  Frieze patterns form a nexus between algebra, combinatorics, and geometry.
T-paths with respect to triangulations of surfaces have been used to obtain
expansion formulae for cluster variables.
  This paper will introduce the concepts of weak friezes and T-paths with
respect to dissections of polygons. Our main result is that weak friezes are
characterised by satisfying an expansion formula which we call the T-path
formula.
  We also show that weak friezes can be glued together, and that the resulting
weak frieze is a frieze if and only if so was each of the weak friezes being
glued.
