1903 East Africa And Protectorate Overprint.

Could anyone told me what the overprint G.E.A. stands for?

Thank you

Sylvain

G.E. A. stands for German East Africa
Your stamp is found in SG Commonwealth catalogue under Tanganyika SG47(1917)

The note in SG under Tanganyika says
British Occupation of German East Africa
Following the invasion of German East Africa by Allied forces civilian mail was accepted by the Indian Army postal service, using Indian stamps overprinted I.E.F. Some offices reverted to civilian control on 1 June 1917 and these used stamps of East Africa and Uganda until the 'G.E.A.' overprints were ready. The last field post offices, in the southern part of the country, did not come under civilian control until 15 March 1919.

The original 1903 stamp showed Edward VII. Your stamp shows George V, so issued under East Africa and Uganda Protectorates in 1912 (SG45) or 1917 (SG45a).