spectrum
in algebraic topology, a sequence of spaces Xᵢ with structure maps ΣXᵢ → Xᵢ₊₁ from (reduced) suspensions, such that its stable homotopy groups can be defined
topological modular form
a (homotopy-theoretic) spectrum, constructed as the global sections of a sheaf of E∞ ring spectra on the moduli stack of elliptic curves, with applications in number theory and string theory