Ukulele into what now?
You may here this term used a lot for all sorts of stringed instruments. The important thing to note is you want good intontation, or perfect intonation. Bad or poor intonation is a bad bad thing, and in extreme cases may mean the uke you have is always going to be unplayable unless you take drastic re-building action.
Anyway, intonation refers to the accuracy of the frets in providing the right notes when fretted. The frets are laid out mathematically to allow for this, but the accuracy depends on their spacing and the distance between the bridge and the nut. Your strings on your standard uke are tuned GCEA when open, but when you fret at certain point, each fretted note should be an accurate note in itself(or its perfect sharp version). If your intonation is off, the thing will sound out of tune, even when tuned (if you follow me)
The way to quickly check intonation on a uke is to tune it, and then fret the string at the 12th fret and play it. The note you hear should be exactly one octave higher than the open string. If it is sharp or flat from the open note, the intonation is off.
What can I do about it?
Well, if the difference is slight, it may be down to the action being too high - I have had ukes where intonation was bad, and I dropped the bridge saddle a millimetre and it sorted it. it may also be a case of action being too high at the nut - be very careful here lower the nut slots too much and it is very hard to go back - you want there to be about a credit cards thickness between the string and the top of the first fret.... It could also be a bad string - try changing it. But if those things dont change it, it could be more serious (ie the bridge is not set in the right place or the frets are poorly spaced) and I would avoid the instrument! Some cheap ukes are just built plain wrong!
Some poorly made instruments have frets that are too high, and fretting firmly can stretch the strings into the gaps giving off notes - this is not a case of bad intonation, but its still a bad set up and I would reject it.
Anyway - no matter what you are spending - if the intonation is off and it is down to the way the thing is built, it will never play right - avoid it!