The infinitive and dictionary form are the same thing. Words (action and descriptive verbs) in this form will all end in 다. It is a base form. That is, other conjugations are all created from these forms of the word. It is not used in speech or writing. Another form ending in 다, the plain form, is however. Here is the infinitive/dictionary form: 먹다 Plain form: 먹는다 Yes, it is confusing because all resources use different terms. It is not that important to know the names of each in my opinion, at least not in English since everyone uses different terms to describe the same thing. There are standard Korean terms for each though. More importantly is to know the ending and what it is used for instead of the name. 먹어 is 반말 ("half words/language"), a very informal way of speaking generally used for animals, friends, children, family members, those younger than you (basically it all depends on your relationship to the speaker)

http://hanguladay.com/tag/infinitive-form/ Well, the above link tell us how to conjugate the predicate with the principle of "모음조화(Vowel Harmon)y". Hence, iIt doesn't explain infinitive form. All dictionary/infinitive form of predicates have to end in the ending '-다'. The ending '-다' is used as the default/basic ending of verbs/adjectives. So, it is known as dictinary form ending or infinitive form ending. And it is also used as a sentence final ending in the declarative in the speech level 해라체 or 하라체. Well, as you know, the predicates in a clause or sentence in Korean can be divided into three types. 1. noun+(이)다 이것은 사과(-이)다. (the present tense in the speech level 해라체) This is an apple. 이것은 어제까지는 사과였다.(or 사과이었다) (the past tense in the speech level 해라체) This was an apple till yesterday. 2. verb 사과를 먹다 (dictionary form) to eat an apple 나는 사과 하나를 먹-는-다. (the present tense of the verb 먹다 in the speech level 해라체 ) I eat an apple. 나는 사과 하나를 먹-었-다. (the past tense of the verb 먹다 in the speech level 해라체) I ate an apple. 3. adjective 사과가 맛있-다. (the present tense of the adjective 맛있다 in the speech level 해라체) Apples are delicious. 그 사과가 맛있-었-다. (the past tense of the adjective 맛있다 in the speech level 해라체) Those apples were delicious.

http://hanguladay.com/tag/infinitive-form/ is wrong. The Korean verbs are composed of "word stem + suffix" infinitive form is composed of "word stem + 다" 먹 is word stem and infinitive/dictionary form is 먹다. There are seven verb paradigms or speech levels in Korean, and each level has its own unique set of verb endings which are used to indicate the level of formality of a situation. 1 Higher levels 1.1 Hasoseo-che 1.2 Hapsyo-che 2 Middle levels 2.1 Haeyo-che 2.2 Hao-che 2.3 Hage-che 3 Lower levels 3.1 Haera-che 3.2 Hae-che These days, some of these speech levels are disappearing from use in everyday life. Hasoseo-che, which is used only in movies or dramas set in older eras, is barely used by modern Koreans, and hage-che exists almost only in novels. In case of 먹다: 먹나이다 (Hasoseo-che) 먹습니다 (Hapsyo-che) = declarative present formal high 먹어요 (Haeyo-che) = declarative present informal high 먹소 (Hao-che) 먹네 (Hage-che) 먹는다 (Haera-che) = declarative present formal low 먹어 (Hae-che) = declarative present informal low Refer to https://en.wikipedia.org/wiki/Korean_speech_levels

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