FLR(O) stands for Further Leave to Remain (Other). The form FLR(O) must be used if you are applying for an extension of stay in the categories of the UK Border Agency immigration rules which are not covered in the Border Agency immigration provisions. Such other reasons include serious medical reasons where the treatment is not private. The ambiguities in UK Immigration rules under the FLR(O) allow the UK Border Agency to set an abstract, high threshold, especially for vulnerable migrants who have a medical condition without considering their economic and social contribution.