  Quantum mechanics predicts that certain stationary potentials can sustain
bound states with an energy buried in the continuous spectrum of scattered
states, the so-called bound states in the continuum (BIC). Originally regarded
as mathematical curiosities, BIC have found an increasing interest in recent
years, particularly in quantum and classical transport of matter and optical
waves in mesoscopic and photonic systems where the underlying potential can be
judiciously tailored. Most of our knowledge of BIC is so far restricted to
static potentials. Here we introduce a new kind of BIC, referred to as Floquet
BIC, which corresponds to a normalizable Floquet state of a time-periodic
Hamiltonian with a quasienergy embedded into the spectrum of Floquet scattered
states. We discuss the appearance of Floquet BIC states in a tight-binding
lattice model driven by an ac field in the proximity of the dynamic
localization regime
