Hello, It means you will own 25% of the property. So if you buy a property for £100,000 you will own 25% of that. If the property increases in price you will have 25% of the capital growth. So if it increases in price by £10,000 then your share would be £2500.00.
The other 75% is owned by the housing accosiation which will charge you rental. Also at a percentage so if the rental for that property is £400 per month they will charge you 75% of that this is £300 per month. Do bear in mind how you fund the other 25% as you have to take those payments in hand to budget costs etc.