These are things named after Jacques Hadamard (1865–1963), a French mathematician. (For references, see the respective articles.)
Cartan–Hadamard theorem
Cauchy–Hadamard theorem
Hadamard product:
entry-wise matrix multiplication
an infinite product expansion for the Riemann zeta function
Hadamard code
Hadamard's dynamical system
Hadamard's inequality
Hadamard's method of descent
Hadamard finite part integral
Hadamard's lemma
Hadamard manifold
Hadamard matrix
Hadamard's maximal determinant problem
Hadamard space
Hadamard three-circle theorem
Hadamard Transform and Hadamard gate
Hadamard–Rybczynski equation
Ostrowski–Hadamard gap theorem
