Technically speaking, ancient Egyptian rulers wre all kings, and pharaoh was more or less a nickname for the ruler which later gradually became an official title.
Pharaoh (/ˈfɛəroʊ/, US also /ˈfeɪ.roʊ/; Coptic: ⲡⲣ̅ⲣⲟ Pǝrro) is the common title now used for the monarchs of ancient Egypt from the First Dynasty (c. 3150 BCE) until the annexation of Egypt by the Roman Empire in 30 BCE, although the term "pharaoh" was not used contemporaneously for a ruler until Merneptah, c. 1210 BCE, during the Nineteenth dynasty, "king" being the term used most frequently until the middle of the Eighteenth Dynasty.
The word pharaoh ultimately derives from the Egyptian compound pr ꜥꜣ, */ˌpaɾuwˈʕaʀ/ "great house", written with the two biliteral hieroglyphs pr "house" and ꜥꜣ "column", here meaning "great" or "high". It was used only in larger phrases such as smr pr-ꜥꜣ "Courtier of the High House", with specific reference to the buildings of the court or palace. From the Twelfth Dynasty onward, the word appears in a wish formula "Great House, May it Live, Prosper, and be in Health", but again only with reference to the royal palace and not the person.
Sometime during the era of the New Kingdom, Second Intermediate Period, pharaoh became the form of address for a person who was king. The earliest confirmed instance where pr ꜥꜣ is used specifically to address the ruler is in a letter to Akhenaten (reigned c. 1353–1336 BCE) that is addressed to "Great House, L, W, H, the Lord". However, there is a possibility that the title pr ꜥꜣ was applied to Thutmose III (c. 1479–1425 BCE), depending on whether an inscription on the Temple of Armant can be confirmed to refer to that king. During the Eighteenth dynasty (sixteenth to fourteenth centuries BCE) the title pharaoh was employed as a reverential designation of the ruler. About the late Twenty-first Dynasty (tenth century BCE), however, instead of being used alone as before, it began to be added to the other titles before the ruler's name, and from the Twenty-Fifth Dynasty (eighth to seventh centuries BCE) it was, at least in ordinary usage, the only epithet prefixed to the royal appellative.
Other notable epithets are nswt, translated to "king"; ḥm, "Majesty"; jty for "monarch or sovereign"; nb for "lord";[note 2] and ḥqꜣ for "ruler".
So "king" is the more or less correct English translation of one title of ancient Egyptian monarchs, while "pharaoh" is the English form of the ancient Egyptian term for the palace, which later became a title for the monarch of Egypt.
And I am not certain whether the Wikipedia pages on Egyptian rulers follow the practices of modern Egyptologists when deciding whether to use pharaoh or king to describe a ruler, and I am not certain if it makes any difference.