[Yandex Cloud documentation](../../../index.md) > [Monium](../../index.md) > Logs > Concepts > Overview and basic concepts

# Overview and basic concepts

Monium Logs is a distributed system for storing, searching, visualizing, and analyzing logs.

Logs are helpful when you need to get insights into your application and infrastructure performance: detect errors and exceptions, investigate incidents, track changes, and find out the causes of degradation.

Monium Logs is part of Monium and shares its basic components such as the project model, access management, data model, and interface.

Monium only accepts OpenTelemetry data. Here is what you can use to send logs:
* OpenTelemetry SDK in the application.
* OTel supported agents: [Otel Collector](../../collector/opentelemetry.md) or [Fluent Bit](../write/fluent-bit.md).

You can use logs together with [traces](../../traces/index.md). To quickly switch between log entries and traces, use `trace_id` and `span_id`.

**Benefits**

* Fast log search for real-time error diagnostics.
* Fault tolerance: data is replicated across data centers.
* Self-monitoring: the system automatically collects incoming log metrics, including the data amount, delivery delays, and number of errors. For diagnostics, there is a [service dashboard](../logs-metrics.md) available with pre-installed charts.

## Basic terms {#terms}

Below are the key terms for setting up and using the system.

### Log line (log record) {#log-row}

The smallest data processing unit in the system. It represents a system event, its description, timestamp, and labels that identify it.

### Log line size {#log-row-size}

Log line size in bytes represents the sum of all top-level field values, as well as the lengths of all keys and values from `labels` and `meta`.

### Event lag {#event-lag}

Event lag is the latency between when the event was generated in the user system and when it was delivered to the centralized logging system (upstream of the collector).

### Observed lag {#observed-lag}

Observed lag is the latency between when the event was first processed by the collection agent and when it was delivered to the centralized logging system (upstream of the collector).

For all terms, see [Overview and basic concepts](glossary.md).