Which word? Situation/Position/Condition
All three nouns are similar in meaning, but they have different nuances or shades of meaning and are used in different contexts in different ways.
Condition
Condition describes the physical state of something or some one. We talk about people or things being in good / bad / terrible / etc condition. Condition can also refer to a health problem:
Considering its age, this house is in excellent condition.
He was in a terrible condition and had drunk far too much whiskey.
She has a severe heart condition and shouldn't be smoking at all.
Conditions (plural) refer to the environment in which something occurs. We talk about things happening in or under appalling / terrible conditions. We also talk about people's living or working conditions:
The rescue was attempted under extremely difficult conditions and with little chance of success.
The refugees were living under appalling conditions with no access to clean water.
Are you happy with your working conditions? ~ Yes, they are excellent. I have no complaints.
The extremely windy conditions made it difficult for either side to play decent football.
Conditions also describe things that must be true or be done before something else can happen. We talk about meeting or satisfying or imposing conditions.
In order to qualify for a grant as a postgraduate student, you will need to satisfy certain conditions.
The conditions imposed by the university meant that no one was likely to qualify.
Terms and conditions describe the business or financial arrangements of an agreement.
Make sure you read the terms and conditions carefully before you take out the student loan
on condition that
Note the expression on condition that for saying that one thing will happen only if another thing happens:
You can have the day off tomorrow on condition that you agree to work on Saturday.
They spoke to the police about the incident on condition that they would not be called as witnesses.
Situation
Situation refers to a set of conditions that are in place at a particular time and in a particular place:
If the situation had been different, our marriage might have succeeded.
I am particularly concerned about the situation in the south of the country where the rules of law and order appear to have broken down.
We also talk about an economic or financial situation:
The financial situation is dire - the company has failed to make a profit in each of the last four years.
situation comedies / situations vacant
Note also the compound nouns situation comedies (abbreviated to sitcoms) which describe amusing television drama series revolving around a set of characters in a family or organisation and situations vacant which refers to a column or page in a newspaper where jobs are advertised:
'The Office' is regarded as one of the most original sitcoms the BBC has produced so far this century.
If you just want a clerical job, look in the situations vacant column in the local newspaper.
position
Position is used in a wider variety of contexts than situation or condition. First and foremost, it refers to the way or where somebody or something is placed.
I was quite badly injured in the demonstration but managed to drag myself to a sitting position under a tree.
This plant loves sunlight and should be placed in an open sunny position in the flower border.
This is quite a detailed map showing the position of all the oil refineries.
Position can also describe a general situation and in this context can sometimes be replaced by situation:
The position / situation is that everyone must be interviewed about the break in by the security services.
If I were in your position / situation, I wouldn't dream of sheltering an escaped convict.
Position also means opinion, i.e. where you stand or are placed, on an issue:
My position on fox hunting is that it is a useful way of keeping the number of foxes down.
Position can also refer to a job in a company, a place in a list or where you play in a team sport such as football:
Is the assistant manager position still open? ~ No, I'm sorry, it's already been filled.
What is their position in the league? ~ They're in forth position at the moment, but if they win today, they'll move up to third.
My best position is on the left in midfield, just in front of the back four.