I. ˌOrdnance ˈSurvey, the abbreviation, OS
an official organization which makes very detailed and correct maps of Britain and Ireland. The maps are used by people walking in the country, and each map has its own OS number. ⇒ compare US Geological Survey

[TahlilGaran] Dictionary of Contemporary English ▲

II. OS /ˌəʊ ˈes/ abbreviation for

1. Ordnance Survey

2. outsize

[TahlilGaran] Dictionary of Contemporary English ▲

OS
Oh Shoot (polite form) 
Old Stuff  
Operating System

[TahlilGaran] Acronyms and Abbreviations Dictionary ▲