In advocating a return to catachesis, J.I. Packer and Gary A. Parrett offer a definition, a set of distinctions, and an overview:

Definition

‘Catechesis is the church’s ministry of grounding and growing God’s people in the Gospel and its implications for doctrine, devotion, duty, and delight.’

Distinctions

1. ‘Procatechesis (or protocatechesis): This refers to catechizing those whom many contemporary church leaders would call “seekers” and whom the ancients might have called “inquirers.”
2. ‘Catechesis proper: This refers to the formal catechetical work of preparing children or adult converts for baptism or confirmation—that is, for their full inclusion in the life of the church.
3. ‘Ongoing catechesis: This refers to the ministry of teaching and formation that really is neverending as believers are continually nurtured in the way of the Lord.’

Overview

1. ‘Catechesis is a thoroughly biblical idea and practice, and we (that is, the evangelical movement as a whole) have strayed grievously from the mandates and models of Scripture in this regard.’
2. ‘The practice of rigorous catechesis has proven to be essential and effective at numerous critical junctures in the life of the church, and there is much to be learned from this history for ministry in contemporary contexts today.’
3. ‘Many forces have conspired to distract most of today’s evangelicals from the biblical business of catechizing, and there are significant consequences that have resulted from our failures in regard to this ministry.’
4. ‘Happily, there are a number of contemporary efforts under way to renew catechetical ministries. These are worthy of our serious observation and, in some cases, emulation.’
5. ‘Catechesis involves instruction that is both ancient and essential. It focuses on the primary doctrines of “the faith that was once for all delivered to the saints” (Jude 3), and especially upon the glorious Gospel of the blessed God. Thus it aims to celebrate and preserve the unity of the church.’
6. ‘Catechesis involves instruction that is holistic. It touches the entire person (and the entire community)—head, heart, and hands; doctrine, experience, and practice.’
7. ‘Catechesis involves instruction that is highly relational and interactive. It is a ministry of the church and must be carried on in the context of the community of faith.’
8. ‘Catechesis involves instruction that is timely and culturally relevant. This ancient faith must always be presented vis-à-vis those alternative claims regarding truth, worldview, and lifestyle that dominate the age and culture in which the church lives.’
9. ‘Catechesis involves instruction that is foundational for faith development throughout one’s life. While catechesis is often associated (and rightly so) with grounding persons in the basics of the faith, it also envisions practices for ongoing learning upon and within those very foundations that have been laid.’

Grounded in the Gospel: Building Believers the Old-Fashioned Way, chapter 1.