Roti means bread in Malay.
While (based on what I've read and seen in Lonely Planet) it may mean different things in other countries, from where I come from (Singapore), roti is basically just another word to refer to your standard loaf of bread.
There are some differences between roti and those pre-sliced nicely-wrapped bundles from the Gardenia factory, however. For one, roti is generally sweeter, and the crust has a peculiar, slightly bitter taste. Its shape is also less rectangular, with more than half of the cross-section being circular. Oh, and it probably doesn't contain seven different vitamins and isn't fortified with iron.
Roti is normally sliced, toasted, and served with some form of spread. The most popular spread would be kaya, which gives rise to the delicious breakfast of roti kaya, or roti pangan as it is oft called.
One interesting thing about the word "roti" is that while it is Malay in origin, most of the older Chinese folks here use the word "loti" while speaking in one of the dialects (usually Hokkien or Teochew). Its meaning is the same as the Malay word it is a corruption of, and the actual Chinese term for bread is hardly ever uttered.