Double taxation is popularly used to indicate taxation of an income two times- by two jurisdictions (countries) when it passes from the source country to the home country. So the topic is related with international flow income (salaries, profit, capital gains etc).
Double taxation issue pops up as the same income is taxed by two countries -the host country where income is generated or the home country where the creator of income is coming from.
Host country is the country where income is generated. It is often called as Country of Source (COS). Home country is the country where the generator of the income is residing. It is otherwise called Country of Residence (COR). There is no international law to avoid double taxation. So, it is for the countries in the international arena to solve double taxation problems by creating bilateral agreements.
