"Ideation" and "concept development" are loose descriptors for the general process of generating and exchanging ideas as part of the marketing process. Ideation sessions are typically conducted among small groups, and can last from a few hours to a few days. The intensity, scope, and duration are dependent upon the category, decision-makers, and opportunity costs of the issue at hand.
Ideation sessions can be conducted at any stage of the product life cycle, from pure innovation and "blue sky" exercise, to product and service development, to refinement, and then production or delivery.
In-depths are conducted using a one-to-one (respondent-moderator) format, and thus generate highly detailed, qualitative (i.e., non-projectable) feedback. In-depths (or "one-on-ones") are a special type of qualitative research.
In-depth interviews are used in specific applications, where we need to understand in great detail the individual thought process and/behaviors that a person experiences in order to understand their journey through a decision-making process. This can include product purchase, use of particular service, or their rationale for deciding upon a course of action.
Focus groups are perhaps the single, best-known marketing research technique. They use the dynamics of group interaction to generate qualitative (i.e., non-projectable) feedback on marketing-related issues, and to develop hypotheses for subsequent quantitative confirmation.
They are most typically used to (1) explore consumer attitudes, motivations, and buying behaviors for new or established products; (2) obtain preliminary reactions to new ideas, product (re)positionings, advertising, product (re)formulations, or packaging prior to additional screening or development work; and (3) develop consumer language for ideas that will then be quantitatively tested.