This type of movement is observed in amoebae (e.g. Amoeba proteus). Their cytoplasm consists of plasmasol (central fluid) surrounded by a more viscous plasmagel. The plasmagel is converted to plasmasol causing the cytoplasm to slide and form a pseudopodium in front to move the cell forward.
Cells that move this way are referred to as amoeboids. Apart from amoeba, other examples are cellular slime moulds (e.g. Dictyostelium discoideum), and human cells, particularly Kupffer cells of liver, monocytes, neutrophils, macrophages, and cancerous cells.