It's a classic Bengali spice-mixture. Literally means five-spices (although different from the Chinese five-spice mix.)
It consists of equal parts of cumin, fennel, fenugreek, nigella and radhuni.
The latter may be hard to get but it's necessary.
Although they ask you to substitute by mustard seeds, radhuni tastes nothing like mustard. It's closer in spirit to celery seeds than anything else.