Risk capital is money that can be lost without jeopardizing ones-self's financial security or lifestyle. Only risk capital should be used for trading purpose and only those with sufficient risk capital should consider trading.
Never ever risk money, that you cannot afford to lose, if you putting your savings from salary, business income which is required for your future you are doing a very big mistake.
Capital or money for trading should only be selected from the money that you have which is extra and it will not effect you in any way if lost, because if you lose money that was very important for you or your kids or your future that will create lot of stress for you.
So always, always only and only trade with money that you have as surplus and is not going to effect you if lost.
Risk capital is money that you want to risk in trading, after you have some profits you can withdraw the original sum and keep trading from profit.
Do not underestimate the importance of this concept, it is extremely important and will effect you severely.