Distance selling is when companies sell their goods online to consumers across EU borders. In order to encourage companies to start trading all across Europe the distance selling thresholds were created. This means that if a company is selling below a specific amount in terms of turnover then they do not have the obligation to register for VAT in that country.
The distance selling thresholds are different for each country and you can find a list of them here.
The moment when a company surpasses the threshold set by the country with which they trade then they must apply for a VAT registration within the same calendar year.