Hello, do you mean the British Imperial Standard? This is standardisation of units established in 1824 to ensure that all countries in the British Empire were "speaking the same language" when it came to things like weight, volume and length.
Under the BIS, weight was measured in ounces, pounds and stones, volume in pints and gallons, and length in inches, feet and miles.
In 1922 the British Empire contained more than 400 million people, a fifth of the world's population, (and that's without America, which gained its independence in 1783). The British like order, so it made sense that someone in South Africa, say, should use the same units as someone in India, Australia or even Canada.
Over the last few decades, many countries chose to adopt a metric system instead (kilograms instead of pounds, litres instead of pints and kilometres instead of miles) since it is considered easier to work out. Now, Britain no longer has an Empire, as such.
In Britian we use both Imperial and metric systems now, depending on what you're doing, which can get a bit confusing.
Hopes this helps.