What Do We Mean by Inflation

What do we mean by inflation?

A) the sudden release of photons when a particle and antiparticle annihilate one another
B) quantum fluctuations by high speed, relativistic particles in a state of false vacuum that caused disturbances in the space- time continuum leading to the process described in the question to which this answer refers
C) the expansion of the universe that we still observe today
D) a sudden and extremely rapid expansion of the universe that occurred in a tiny fraction of a second during the universe's first second of existence