What modern-day nations constitute the Senegambia region today?

On Wikipedia it says, "The region encompasses the modern states of Senegal, The Gambia, and Guinea-Bissau, as well as portions of Mauritania, Mali, and Guinea." However, I was told to not always take information from Wikipedia.
An Oxford bibliography states, "Senegambia, strictly speaking, comprises the nations of Senegal and The Gambia, although southern Senegal and the adjacent nation of Guinea-Bissau (Guiné-Bissau in Portuguese) have much in common in terms of climate and geography. "
I don't really know the difference between nation and countries because it says Senegal and Gambia are countries on some sites while on others they are nations.
Which ones should I use?

For most purposes, country and nation are used interchangeably.

Let me see

Understanding the terminology can help clarify the difference between "nations" and "countries." Generally, a nation refers to a distinct group of people sharing common cultural and historical characteristics. On the other hand, a country is a political and geographical entity recognized by the international community.

Regarding the Senegambia region, both sources you mentioned provide slightly different perspectives. Wikipedia states that the region encompasses Senegal, The Gambia, Guinea-Bissau, as well as portions of Mauritania, Mali, and Guinea. However, as you pointed out, Oxford bibliography specifically mentions that Senegambia, strictly speaking, comprises Senegal and The Gambia, with the addition of southern Senegal and Guinea-Bissau due to shared climate and geography.

Since there may be differing opinions and interpretations, it is always recommended to consult multiple reliable sources to establish a comprehensive understanding. Apart from Wikipedia and the Oxford bibliography, you can explore other credible references, such as books, academic journals, or governmental websites, to gain a more well-rounded perspective on the topic.