"Inflationary periods" refers to periods of time when the general level of prices for goods and services rises, and the purchasing power of money decreases. It means things tend to become more expensive over time. Full definition
For example, during inflationary periods in the 1960s, commodities outperformed the equity market, while energy companies underperformed. (fidelity.com)
«New theory of secondary inflation expands options for avoiding an excess of dark matter: Physicists suggest a smaller secondary inflationary period in the moments after the Big Bang could account for the abundance of the mysterious matter.» (sciencedaily.com)
«If this secondary inflationary period happened, it could be characterized by energies within the reach of experiments at accelerators such as the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider,» he said. (sciencedaily.com)