For storing your images with no loss in quality (if this is what you wanted to do) I recommend .png. You can make the size smaller than .bmp and the image will still be 100% perfect.
A longer explanation:
Uncompressed
Not compressed. Not made smaller. If we are dealing with Images then I believe .bmp is the only (or at least the most 'common') uncompressed format available. Not recommended for nearly any use these days. To make a metaphore we could say that if we wanted to leave a blanket uncompressed, we would do nothing to the blanket and just spread it out like normal.
Compressed
File has been made smaller. Can be one of two general styles of compression: Lossless or lossy. Both make the file smaller but in different ways. Lossy generally makes the file much smaller than lossless but loses information about the original. Lossy compression is used with media files much more often than lossless.
Lossless
Does not lose any of the original information. The original uncompressed file can be reassembled from this. If we are talking about images the most common format is .png. If it's just generic files the most common is .zip. To continue the blanket metaphore: if we wanted to compress the blanket in a lossless way we would fold it a few times so it is smaller.
Lossy
Loses information about the original to save space. Images and music and video are commonly compressed in a lossy way. Information about the original file is irreversibly lost. In music for instance when compressing in a lossy manner we might lose the very high or the very low notes on the assumption that most of us wouldn't hear them anyway. For music .mp3 is the most common, and for images .jpg/.jpeg (same thing) is most common. For video, the file extension doesn't represent the way it was compressed -- the file type is just a 'container' for video and audio media. A few common methods of video compression are divx (not used these days) xvid (falling out of favor but still used) and h264 (new and gaining favor) with .avi being the most common container. You cannot use lossy compression on non-media files; it will break them because all of the information is needed. An example of lossy 'compression' of the blanket could be cutting the edges of the blanket until it fits on your bed perfectly, then folding it up.
3The BMP format is both lossless and uncompressed, and can still be compressed in say an archive, making it lossless only. They compress up well in a compression archive. – Psycogeek – 2012-02-04T21:12:38.560
Is BMP the only uncompressed image format around? – user1032421 – 2012-02-04T21:29:14.507
Not necessarily -- both GIF and TIFF have uncompressed options. – Mike Scott – 2012-02-04T21:32:16.873
Sorry, I don't understand how BMP is both lossless and uncompressed file format. How I understand is that a file can be either uncompressed or compressed (lossless), so how can it be both? – user1032421 – 2012-02-05T00:41:07.030
@user1032421 Sure, use of the word "lossless" is used to define a compression that is lossless, "lossless compression" even though it it applied in some situations were there can be minor loss, Better termed LessLoss :-) If you want to get all technical definitiony your right. but the reality of it is more important than the Hypewords. They dont toss stuff out to save data. – Psycogeek – 2012-02-05T02:13:55.113
3@user1032421 Pretty much every uncompressed format is lossless. – David Schwartz – 2012-02-05T02:16:46.847
@user1032421: For that explanation, you should google as there are 100000000000 different and good explanations. The quick and dirty way is to think of a file as a set of 10 remotes. A lossless compression is getting one universal remote, that does everything. So you have one power button that works for all your devices. A lossy compression is "I can live without these five remotes" so you throw out those five. Either way you have a smaller set of remotes. – surfasb – 2012-02-05T02:19:01.440