A high-pass filter (HPF) is a EQ filter that let's all high frequencies pass through unaffected, but cuts the low frequencies. For this reason, it is also sometimes referred to as a low cut filter.
On hardware mixers, a high pass filter set to a particular frequency is common. This most often is set at 75 Hz. Some hardware units and most software EQ's, however, will allow you to choose what frequency you want the filter to start at. Some will also allow you to configure the amount the frequency drops off below that point.