In short
ISO is an independent organisation that publishes international standards for management systems and technical topics; ISO 9001 covers quality, ISO 14001 environment, ISO 45001 occupational health and safety and ISO 27001 information security.
ISO management system standards share a common structure: context, leadership, planning, support, operation, performance evaluation and improvement, so several standards can run in one integrated management system.
Certification is granted through audits by accredited bodies, which expect evidence of records, document control and corrective actions.