Depression and anticyclone কী?

Example 25.7 (Reading a barometer’s record)

For the first 8 hours the pressure rises to about $1031\,\mathrm{hPa}$: the anticyclone passes over S, with settled weather. Then it falls for 30 hours, by about $45\,\mathrm{hPa}$: the depression is coming. It falls fastest a few hours before the warm front passes, more slowly in the warm air behind it, and reaches its lowest, about $986\,\mathrm{hPa}$, just as the cold front passes. Then it rises: the depression is moving away, and the cooler, clearer air behind the cold front arrives.