der Leiter
leader
A person who leads a group, department, or organization and is responsible for it.
Der Leiter der Marketingabteilung hat das neue Projekt vorgestellt.
The head of the marketing department presented the new project.

leader / conductor
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leader
A person who leads a group, department, or organization and is responsible for it.
Der Leiter der Marketingabteilung hat das neue Projekt vorgestellt.
The head of the marketing department presented the new project.

The noun 'der Leiter' is derived directly from the verb 'leiten' (to lead / to conduct). This connection helps you understand all the meanings: a person leads a group, and a material conducts electricity or heat.
Wer leitet dieses Projekt?
Who is leading this project?
You can tell from the context whether a person or a material is meant. If it is about companies, departments, or teams, it is a person. If it is about physics, technology, or materials like metals, it is an electrical or thermal conductor.
Der Leiter unserer Personalabteilung geht bald in Rente.
The head of our HR department is retiring soon.
To say what a person leads, the genitive or the preposition 'von' with the dative is usually used. So the structure is 'Leiter des/der...' (head/leader of the...) or 'Leiter von...' (head/leader of...).
Er ist der Leiter des Chors.
He is the leader of the choir.
In the physical meaning, 'Leiter' is often combined with an adjective that describes the property. Common combinations are 'elektrischer Leiter' (electrical conductor), 'guter Leiter' (good conductor), or 'schlechter Leiter' (poor conductor).
Gold ist ein sehr guter elektrischer Leiter.
Gold is a very good electrical conductor.
president
'der Präsident' and 'der Leiter' can both refer to a person who has responsibility for a group or organization. 'der Leiter' is a general word and fits many areas, for example a department, a project, or a course. 'der Präsident' is more strongly an official title, often in a club, an institution, or a large organization. If the point is simply who leads or organizes things day to day, 'Leiter' sounds more natural. If the person holds an official high-level title, 'Präsident' fits better.

Nach der Besprechung spricht der Mitarbeiter mit dem Leiter der Abteilung.
After the meeting, the employee speaks with the head of the department.
Der Präsident des Sportvereins begrüßt die Gäste vor dem Fest.
The president of the sports club welcomes the guests before the celebration.