Galoshes are rubber shoes you pull on over your ordinary shoes when the street is wet or snowy, so your real shoes stay dry. Though actually, they are not the same as rain boots, which you wear instead of shoes. You can say a galosh for one, but people almost always talk about them as a pair. The word sounds a bit old now; younger speakers more often say waterproof boots, or just rain boots. The idea is still useful. The word itself has grown a little old-fashioned.