In Jainism, “yuglik” (युगलिक / युगलिक जीव) means a very special kind of twin human beings described in Jain cosmology and time‑cycle.

Below is a simple but detailed explanation.

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1. Basic meaning

• Yuglik = a pair (yugal) of twins
• Always one boy + one girl born together.
• They live together for their whole life.
• They are considered a special human form that existed only in the very early ages of the world.

So, whenever you hear “yugliks” in Jainism, think of male–female twin pairs with very long lives and very mild karmas, described in Jain scriptures about ancient times.

You can also read a brief definition here

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2. In which time period do yugliks exist?

Jain time is divided into 6 aras (time‑periods) in every half‑cycle (avasarpini and utsarpini).

In our current half‑cycle (avasarpini):

1. Suṣama‑suṣamā (1st era – best happiness)
2. Suṣama (2nd)
3. Suṣama‑duḥṣamā (3rd)
4. Duḥṣama‑suṣamā (4th)
5. Duḥṣama (5th – present)
6. Duḥṣama‑duḥṣamā (6th – worst misery)

Yugliks are found in the very early eras, especially in:

• 1st era (Suṣama‑suṣamā)
• 2nd era (Suṣama)
• and up to around the 3rd era (Suṣama‑duḥṣamā)

After that, this yuglik type of birth disappears. In our current 5th era, there are no yugliks at all according to Jain cosmology.

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3. Nature and lifestyle of yugliks

(a) Long life and mild karma

• Yugliks are said to have extremely long life‑spans (lakhs of years, etc., depending on the era).
• They experience very little pain or trouble.
• Their karmas are generally mild, so:

- no major diseases, - no big sorrows, - life is very easy and comfortable.

This is because the early eras of the time‑cycle are full of natural happiness, and yugliks are a product of that very pure environment.

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(b) Relationship between the twins

At the start of life:

• They are like brother–sister twins, always together,
• They share food, house, comforts, etc.

Later in life:

• As they grow and their karmas mature, their relation gradually shifts:

- from a simple twin companionship - to a married‑like pair, and - then they produce children – which again include yuglik twins.

So, one pair of yugliks gives rise to the next generation of yugliks.

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(c) Physical & social conditions

Traditional Jain texts describe people of those eras (including yugliks) as:

• Very tall,
• Strong and beautiful,
• Very healthy,
• With natural food provided by wish‑fulfilling trees (kalpavṛkṣa).

There was:

• No agriculture,
• No business,
• Almost no organized society, no war, no crime.

Life was simple, comfortable and almost effortless. Yugliks are part of this golden‑age picture.

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4. Spiritual aspect of yugliks

• In those early eras, Jain dharma in the full structured form (like today) had not yet started.
• The level of passions (kaṣāyas) like anger, pride, deceit, greed was very low.
• So, although yugliks were not yet following vows like a monk or shravak, their natural inner state was calmer and purer than most people today.

Later, as eras decline:

• Lifespan shortens,
• Passions increase,
• Yugliks disappear,
• And then Tirthankars such as Bhagwan Ṛṣabhdev (Adinath) appear and organize dharma for more complex, passion‑filled societies.

So yugliks represent a natural, simple, low‑passion human life‑form before the world becomes spiritually and socially complex.

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5. Scriptural / traditional context

• The concept of yugliks appears in Jain cosmological and time‑cycle descriptions (Digambar and Shwetambar both accept yuglik‑type beings, though names/pronunciation can vary: yuglik, yugalik, juyalik, juyalag etc.).
• They are mentioned when explaining:

- The early eras, - Human forms of those eras, - How population and society gradually change as time moves from sukh (happiness) towards dukh (suffering).

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6. Summary in very simple words

• Yugliks are:

- Special male–female twins, - With very long, easy, comfortable lives, - Existing only in the very early, happiest eras of the Jain time‑cycle.

• They:

- Stay together for life, - Later live almost like a married couple, - And give birth to more yuglik twins.

• In our current era, yugliks do not exist; they are part of the ancient human conditions described in Jain cosmology.

You can also see a concise explanation here