It's literally freezing in there.
It's practically freezing in there.
It's virtually freezing in there.
You may have seen sentences similar to these used every now and then. The words, literally, practically, and virtually, are all used in these instances to convey emphasis to what's being said. For this need for emphasis, literally and virtually were originally used a lot, but somehow practically also found its way to this and is getting popular.
But despite this common meaning, each of these words has its specific place in English; let's see it now.
Literally has actually held the meaning, "in a manner that accords with the literal sense of the words", as the American Heritage Guide tells. In that sense, we should not be using literally in the sentence above. But it went on to be used as a word for emphasis and stayed so.
But actually, literally should not be used when a metaphor is present, as in the above sentence. A way to know this is to assume that literally has the same meaning as 'really'. Then substitute in the above sentence, it becomes, "It's really freezing in here", which is untrue. Literally, hence, should be used when you mean 'really', and not when you want mere emphasis. Examples:
There are literally thousands of members in his party. [There are really at least a thousand members in the party]
He spent literally five hours waiting for her. [Not that he spent four and a half hours]
Practically has a word-by-word meaning of "almost" or "in a practical way". Example:
He lives his life practically, so he gets into as few troubles as possible.
The word, as the Heritage Guide tells, has the extended meaning, "for all practical purposes", which gives the following example sentences:
The city was practically unapproachable before the ceasefire.
In this sentence, we are not giving an emphasis, but we are referring to a practical situation, which somehow has a bit of emphasis.
The trick to using practically in this sense, and not to get lost in the above 'emphasis' meaning, is to substitute it with its meaning "for all practical purposes". Let's see how:
It's, for all practical purposes, freezing in here.
Now, as in the case of 'literally', you know this isn't the case. So, this sentence is wrong. Use practically when you have a meaning similar to 'really'. Examples:
The job of a military nurse is practically unsafe for her.
The house was practically unapproachable after the fire.
Virtually is safe to be used with all sentences that require a metaphorical emphasis, as in the above sentence as well as the following examples.
Her married life is virtually a chasm of darkness.
There's virtually no air in the cabin.
All we found in the party were virtually two people, she and her husband.
Dictionaries tell, virtually means, "in effect even if not in fact", and "nearly".