For us Japanese, this is one of the most frequently asked yet difficult to answer word :) Because we don't have the exact translation for this. But this is a very useful word to cheer someone who is willing to achieve something or some goal. Maybe phrases like "Go for it!" or "Hang in there!" are close, showing that your thoughts are with them.

This kind of phrases are very common in Japan; this is called a 'nuance' word-words without specific definitions but has several meanings! Ganbatte kudasai stands for 'please do your best' or 'keep it up' or 'I know you can do it' - it should be used depending on situations but they are usually used whenever someone is attempting to do or face something like and exam or giving a talk/speech in front of many people (kudasai is also a nuance word for 'please'). In English, I think the best translation would be "Good luck" but it does not completely mean that. The previous answers were also correct! ^_^ (in hiragana it is written like this: がんばってください)...

Keep at it and do your best. Used to cheer somebody on.