The Finnish words kassi, laukku, pussi, and säkki can all be translated into English as "bag". Even though there are no clear-cut distinctions between them, they refer to different kinds of bags, and usually only one of them is used for certain kinds of bags, e.g. ostoskassi (shopping bag), hedelmäpussi (plastic bag for fruits and vegetables), viljasäkki (bag of grain), and matkalaukku (suitcase).
Both kassi and laukku refer to bags used to carry personal items, and such bags therefore normally have a handle, whereas a pussi and a säkki usually don't. A kassi is made of textile, plastic, paper, or other soft material whereas a laukku is made of stiffer and heavier (leather, strong textile), even hard material, as long as its main purpose remains the same. In English, one would use the word "case" or, more commonly, compound nouns such as "briefcase" for this kind of laukku. A pussi or a säkki is normally a bag used for packaging and storage, the main difference between them being the size, and secondarily, the heaviness of the material used. A säkki is larger and is usually called a "sack" in English.