Calling Swedboy - what is horticultural grit?

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I was advised to repost with a specific forum member in mind, so here goes (again...):

I live in Sweden, watch Gardener's World, and have asked various gardening sites over here what horticultural grit might be, and where can I buy it. Problem is, over here, they've never heard of it - google translates it to "trädgårdsgrus", which is basically the gravel you put down in walkways. 

I think it'd be great to have some to lighten up the soil, but please, can someone explain what it is, where it comes from, and how I might get some over here in the lovely land of the swedes...