You have omitted "interamente" which would be "fully". In the UK and often in the US (depends on the state, I think), if a company makes losses, its equity and eventually even its share capital may diminish and even become negative. If the company still has funds to pay creditors, it can continue in business. In Italy "negative equity" is not allowed. If losses are made, money must be paid in to replenish the losses and maintain the share capital intact, hence the word "esistente". It still exists and hasn't been drawn on.
Available share capital and reserves would mean available for the payment of dividends. In Italy a company must maintain "compulsory reserves". No company's equity is always available for dividend payments.