This adverb applies to anything that is happening more often, in greater numbers, or with greater intensity. An increasingly hot summer keeps getting hotter.
To increase something is to add to it numerically, like increasing the size of your family by having a baby. Anything that happens increasingly is growing in some way. An increasingly depressed person keeps getting sadder. An increasingly sick patient keeps getting worse. An increasingly corrupt government is getting less and less honest. When you see this word, you know something is intensifying.