Add initial glossary

content/docs/introduction/glossary.md

+---
+title: Glossary
+sort_rank: 8
+---
+
+# Glossary
+
+
+### Alert
+
+An alert is the outcome of an alerting rule in Prometheus that is
+actively firing. Alerts are sent from Prometheus to the Alertmanager.
+
+### Alertmanager
+
+The [Alertmanager](../../alerting/overview/) takes in alerts, aggregates them into
+groups, de-duplicates, applies silences, throttles, and then sends out
+notifications to email, Pagerduty, Slack etc.
+
+### Bridge
+
+A bridge is a component that takes samples from a client library and
+exposes them to a non-Prometheus monitoring system. For example the Python
+client can export metrics to Graphite.
+
+### Client library
+
+A client library is a library in some language (e.g. Go, Java, Python, Ruby)
+that makes it easy to directly instrument your code, write custom collectors to
+pull metrics from other systems and expose the metrics to Prometheus.
+
+### Collector
+
+A collector is a part of an exporter that represents a set of metrics. It may be
+a single metric as part of direct instrumentation, or many metrics if it is pulling
+metrics from another system.
+
+### Direct instrumentation
+
+Direct instrumentation is when instrumentation is added inline as part the source code
+of a program.
+
+### Exporter
+
+An exporter is a binary that exposes Prometheus metrics, commonly by converting
+metrics that are exposed in a non-Prometheus format into a format Prometheus supports.
+
+### Notification
+
+A notification represents a group or one of more alerts, and is sent by the Alertmanager
+to email, Pagerduty, Slack etc.
+
+### Promdash
+
+[Promdash](../../visualization/promdash/) is a Ruby-on-Rails dashboard builder for Prometheus.
+It is similar at a high-level to Grafana, but is specific to Prometheus.
+
+### Prometheus
+
+Prometheus usually refers to the core binary of the Prometheus system. It may
+also refer to the Prometheus monitoring system as a whole.
+
+### PromQL
+
+[PromQL](../../querying/basics/) is the Prometheus Query Language. It allows for
+a wide range of operations including aggregation, slicing and dicing, prediction and joins.
+
+### Pushgateway
+
+The [Pushgateway](../../instrumenting/pushing/) persists the most recent push
+of metrics from batch jobs. This allows Prometheus to scrape their metrics
+after they have terminated.
+
+### Silence
+
+A silence in the Alertmanager prevents alerts with labels matching the silence from
+being included in notifications.
+
+### Target
+
+One application, server or endpoint that Prometheus is scraping.