I think this information is very useful for foreigners who are staying or planning to come to Korea.
For who wish to stay and extend visa in Korea, you have one way that is you have to change your visa.
If you don't know what to, here is the types of visa intention, explanation of letters and numbers on your ID Alien Card.
Korean Visa types:
1. A-1 Diplomat (외교)
A-2 Government Official (공무)
A-3 Treaty (협정)
2. B-1 Visa Exempted (사증면제)
B-2 Tourist/Transit (관광통과)
Note: The B-2 status allows travellers who are passport holders of various jurisdictions, including the People's Republic of China mainland, to stay in South Korea for a maximum period of 30 days, provided that they are using Incheon International Airport as a transit stopover.
3. C-1 Short-Term News Coverage Activities C-1 (일시취재)
C-2 Short-Term Business Visitor (단기상용)
C-3 Short-Term General (Tourist) (단기종합)
C-4 Short-Term Employment (단기취업)
4. E-1 University Professor (교수)
E-2 Foreign Language/ English Conversation Teacher (회화지도)
E-3 Researcher (연구)
E-4 Technical Instructor (기술지도)
E-5 Professional Consultant (전문직업)
E-6 Entertainer (예술흥행)
E-7 Specially Designated Profession (특정활동)
E-8 Employed Trainee (연수취업)
E-9 Non-professional Employment (비전문취업)
E-10 Vessel Crew (내항선원)
5. F-1 Visiting or Joining Family (방문동거)
F-2 Long-Term Resident (거주)
F-3 Accompanying Spouse (동반)
F-4 Overseas Korean (재외동포)
F-5 Permanent Foreign Resident (영주)
F-6 Foreign Spouse (국민의 배우자) - replaces F-2-1 visa
6. G-1 Others/Miscellaneous
7. H-1 Working holiday (관광취업)
H-2 Working visit (방문취업제)