Adding to rmw's comments, some combustion turbine plants exist for the primary purpose of serving as spinning reserve. Their fast start and fast loading capability allows them to reach full load fast enough to satisfy their spinning reserve rating while being at rest. This permits other units, typically nuclear or coal, to operate at higher, more efficient loadings while the GT plant consumes no fuel. Each start for these plants is brutal, but since relatively few starts are involved, these plants can be very effective both economically and environmentally. These plants almost always use light fuel oil stored on site for the sake of having an assured fuel supply. They are very costly when they run, but they make lots of money or save lots of fuel when they are not running. Their economics can be astoundingly strong. The base load for these plants may seem relatively high, but this is based on a relatively short operating life.
In other cases, the exhaust from a combustion turbine may be used in a process plant. In these cases, the operating temperatures may be unusually low and the operating life can be amazingly long. The seemingly low generating efficiency is more than compensated by the use of the exhaust heat.
As others have indicated, the true meaning of base load is very much application specific.