na-adjective
Describes something that produces a desired result or works well in practice. Often used for methods, measures, presentations, and strategies.
この方法はとても効果的だ。
This method is very effective.
効果的なプレゼンのコツを教えてください。
Please tell me some tips for an effective presentation.
効率的 means 'efficient' (achieving maximum productivity with minimum wasted effort), whereas 効果的 means 'effective' (producing a desired result regardless of resource use).
Compound of 効果 (effect, result) + 的 (-like, -ive). The suffix 的 derives from Chinese and forms adjectival nouns.