I'd like to nuance this position slightly.
While it can be said that nations without a state religion can be called secular nations, we do have to look the deeper mechanics. Important in this perspective is how the state relates to the different religions. I will take Belgium as an example here, because I am most familiar with its laws and regulations.
Belgium is de jure a secular nation, but de facto a Roman Catholic nation. While Belgium knows a separation of church and state, the state does 'recognize' certain religions. Gaining state recognition means that a religion is subsidized. Subsidization is provided for Roman Catholics, Orthodox, Protestants, Muslims, Jews, and 'freethinkers'. For all groups, except for Roman Catholics, the subsidy is calculated on the basis of member count. For Roman Catholicism subsidy is calculated on the basis of population of each Belgian community. This gives the Roman Catholic Church an enormous advantage: the actual number of adherents to the Catholic faith is of no real importance, subsidy is guaranteed on the basis of population count.
So, I contend that the label of 'secular nation' can actually mask mechanisms that give some groups an advantage.