What does «susceptible» mean in Spanish?

That can be modified. Capable of receiving modifications (not by itself).

Examples of use in Spanish: "plan susceptible de modificarse".

"susceptible de mejora".
Easily offended, sensitive, fussy, prickly, itchy.

Examples of use in Spanish: "eres muy susceptible".
Vulnerable, sensitive, exposed or predisposed.

Examples of use in Spanish: "El remedio puede presentar reacciones adversas en personas susceptibles".