The most appropriate phrase to describe this process is boiling without actually boiling, if such an expression really makes sense.
The term to poach is used to indicate all the procedures of slow cooking which takes place in a liquid, no matter how small the amount. Thus it is that the term is applicable to the cooking of large cuts of turbot and salmon in a Court-bouillon, equally as well as for fillets of sole poached in a small quantity of fish stock, and to hot Mousses and Mousselines, Quenelles, Creams and Royales.