Achalgachchh and Tapagachchh are two different Shwetambar Jain gacchas (monastic lineages), and both follow Jain Dharma. The main differences are in history, lineage, and monastic tradition, not in the basic Jain principles of Ahimsa, Satya, Aparigraha, and Moksha.

1. Tapagachchh

• It is one of the most well-known and widely followed Shwetambar gacchas.
• It became especially prominent through Acharya Jagatchandra Suri and later great acharyas.
• The name “Tapa” refers to austerity and penance.
• Tapagachchh monks are traditionally known for strict discipline, tapasya, and organized monastic order.
• Many major Shwetambar temples and murtipujak traditions are historically connected with Tapagachchh.

2. Achalgachchh

• Achalgachchh is also a Shwetambar Jain gaccha.
• The name “Achal” means steadfast, firm, or unwavering.
• It is considered an older and respected monastic tradition.
• This gaccha is known for its own line of acharyas and disciplined practice.
• It is less widespread than Tapagachchh in many places, but it has its own important historical identity.

Simple difference

• Tapagachchh emphasizes tapasya and became a larger, more widespread monastic tradition.
• Achalgachchh emphasizes steadfastness and firmness in conduct and has a distinct lineage.

Important point

Both are within Jainism, and both accept the same core Jain values. The difference is mainly in gaccha tradition, historical development, and monastic lineage.

If you want, I can also explain the difference in monastic rules, history, and famous acharyas of both.